EP1438054A1

EP1438054A1 - Methods and compositions for treating flaviviruses and pestiviruses using 4'-modified nucleoside

Info

Publication number: EP1438054A1
Application number: EP02770551A
Authority: EP
Inventors: Gilles Gosselin; Jean-Louis Imbach; Jean-Pierre Sommadossi
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite de Montpellier; Idenix Cayman Ltd
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite de Montpellier; Idenix Cayman Ltd
Priority date: 2001-09-28
Filing date: 2002-09-30
Publication date: 2004-07-21
Also published as: JP2005536440A; EP1438054A4; US20040006002A1; WO2003026675A1; UY27465A1

Abstract

A method and composition for treating a host infected with flavivirus or pestivirus comprising administering an effective flavivirus or pestivirus treatment amount of a described 4'-modified nucleoside or a pharmaceutically acceptable salt or prodrug thereof, is provided.

Description

METHODS AND COMPOSITIONS FOR TREATING

FLAVIVIRUSES AND PESTIVIRUSES USING 4'-

MODLFIED NUCLEOSIDE

FIELD OF THE INVENTION

This invention is in the area of pharmaceutical chemistry, and in particular, is a compound, method and composition for the treatment of flaviviruses and pestiviruses. This application claims priority to United States Patent Application No. 60/326,192.

BACKGROUND OF THE INVENTION

Pestiviruses and flaviviruses belong to the Flaviviridae family of viruses along with hepatitis C virus. The pestivirus genus includes bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV, also called hog cholera virus) and border disease virus (BDV) of sheep (Moennig, V. et al. Adv. Vir. Res. 1992, 41, 53-98). Pestivirus infections of domesticated livestock (cattle, pigs and sheep) cause significant economic losses worldwide. BVDV causes mucosal disease in cattle and is of significant economic importance to the livestock industry (Meyers, G. and Thiel, H.-J., Advances in Virus Research, 1996, 47, 53- 118; Moennig V., et al, Adv. Vir. Res. 1992, 41, 53-98).

Human pestiviruses have not been as extensively characterized as the animal pestiviruses. However, serological surveys indicate considerable pestivirus exposure in humans. Pestivirus infections in man have been implicated in several diseases including congenital brain injury, infantile gastroenteritis and chronic diarrhea in human immunodeficiency virus (HIV) positive patients. M. Giangaspero et al., Arch. Virol. Suppl, 1993, 7, 53-62; M. Giangaspero et al., Int. J. Std. Aids, 1993, 4 (5): 300-302.

The flavivirus genus includes more than 68 members separated into groups on the basis of serological relatedness (Calisher et al., J. Gen. Virol, 1993, 70, 37-43). Clinical symptoms vary and include fever, encephalitis and hemorrhagic fever. Fields Virology, Editors: Fields, B. N., Knipe, D. M., and Howley, P. M., Lippincott-Raven Publishers, Philadelphia, PA, 1996, Chapter 31, 931-959. Flaviviruses of global concern that are associated with human disease include the dengue hemorrhagic fever viruses (DHF), yellow fever virus, shock syndrome and Japanese encephalitis virus. Halstead, S. B., Rev. Infect. Dis., 1984, 6, 251-264; Halstead, S. B., Science, 239:476-481, 1988; Monath, T. P., NewEng. J. Med., 1988, 319, 641-643.

Examples of antiviral agents that have been identified as active against the flavivirus or pestiviruses mclude:

(1) interferon and ribavirin (Battaglia, A.M. et al, Ann. Pharmacother, 2000,. 34, 487-494); Berenguer, M. et al. Antivir. Ther., 1998, 3 (Suppl. 3), 125-136);

(2) Substrate-based NS3 protease inhibitors (Attwood et al, Antiviral peptide derivatives, PCT WO 98/22496, 1998; Attwood et al, Antiviral Chemistry and Chemotherapy 1999, 10, 259-273; Attwood et al, Preparation and use of amino acid derivatives as anti-viral agents, German Patent Pub. DE 19914474; Tung et al. Inhibitors of serine proteases, particularly hepatitis C virus NS3 protease, PCT WO 98/17679), including alphaketoamides and hydrazinoureas, and inhibitors that terminate in an electrophile such as a boronic acid or phosphonate (Llinas-Brunet et al, Hepatitis C inhibitor peptide analogues, PCT WO 99/07734).

(3) Non-substrate-based inhibitors such as 2,4,6-trihydroxy-3-nitro- benzamide derivatives (Sudo K. et al, Biochemical and Biophysical Research Communications, 1997, 238, 643-647; Sudo K. et al Antiviral Chemistry and Chemotherapy, 1998, 9, 186), including RD3- 4082 and RD3-4078, the former substituted on the amide with a 14 carbon chain and the latter processing apαr -phenoxyphenyl group;

(4) Thiazolidine derivatives which show relevant inhibition in a reverse- phase HPLC assay with an NS3/4A fusion protein and NS5A/5B substrate (Sudo K. et al, Antiviral Research, 1996, 32, 9-18), especially compound RD- 1-6250, possessing a fused cinnamoyl moiety substituted with a long alkyl chain, RD4 6205 and RD4 6193;

(5) Thiazolidmes and benzanilides identified in Kakiuchi N. et al. J. EBS Letters 421, 217-220; Takeshita N. et al. Analytical Biochemistry, 1997, 247, 242-246;

(6) A phenanthrenequinone possessing activity against protease in a SDS- PAGE and autoradiography assay isolated from the fermentation culture broth of Streptomyces sp., Sch 68631 (Chu M. et al, Tetrahedron Letters, 1996, 37, 7229-7232), and Sch 351633, isolated from the fungus Penicillium griscofuluu n, which demonstrates activity in a scintillation proximity assay (Chu M. et al, Bioorganic and Medicinal Chemistry Letters 9, 1949-1952);

(7) Selective NS3 inhibitors based on the macromolecule elgin c, isolated from leech (Qasim M.A. et al, Biochemistry, 1997, 36, 1598-1607);

(8) Helicase inhibitors (Diana G.D. et al, Compounds, compositions and methods for treatment of hepatitis C, U.S. Pat. No. 5,633,358; Diana G.D. et al, Piperidine derivatives, pharmaceutical compositions thereof and their use in the treatment of hepatitis C, PCT WO 97/36554); (9) ■ Polymerase inhibitors such as nucleotide analogues, gliotoxin (Ferrari

R. et al. Journal of Virology, 1999, 73, 1649-1654), and the natural product cerulenin (Lohmann V. et al., Virology, 1998, 249, 108-118);

(10) Antisense phosphorothioate oligodeoxynucleotides (S-ODN) complementary to sequence stretches in the 5' non-coding region (NCR) of the virus (Alt M. et al, Hepatology, 1995, 22, 707-717), or nucleotides 326-348 comprising the 3' end of the NCR and nucleotides 371-388 located in the core coding region of the IICV RNA (Alt M. et al, Archives of Virology, 1997, 142, 589-599; Galderisi U. et al, Journal of Cellular Physiology , 1999, 181, 251-257);

(11) Inhibitors of IRES-dependent translation (Ikeda N et al, Agent for the prevention and treatment of hepatitis C, Japanese Patent Pub. JP- 08268890; Kai Y. et al. Prevention and treatment of viral diseases, Japanese Patent Pub. JP-10101591);

(12) Nuclease-resistant ribozymes (Maccjak, D. J. et al, Hepatology 1999, 30, abstract 995); and

Other miscellaneous compounds including 1 -amino-alkylcyclohexanes (U.S. Patent No. 6,034,134 to Gold et al), alkyl lipids (U.S. Patent No. 5,922,757 to Chojkier et al), vitamin E and other antioxidants (U.S. Patent No. 5,922,757 to Chojkier et al), squalene, amantadine, bile acids (U.S. Patent No. 5,846,964 to Ozeki et al), N-(phosphonoacetyl)-L-aspartic acid, (U.S. Patent No. 5,830,905 to Diana et al), benzenedicarboxamides (U.S. Patent No. 5,633,388 to Diana et al), polyadenylic acid derivatives (U.S. Patent No. 5,496,546 to Wang et al), 2',3'- dideoxyinosine (U.S. Patent No. 5,026,687 to Yarchoan et al), and benzimidazoles (U.S. Patent No. 5,891,874 to Colacino et al).

Idenix Pharmaceuticals, Ltd. was first to disclose branched nucleosides, and their use in the treatment of HCV and flaviviruses and pestiviruses in International Publication Nos. WO 01/90121 and WO 01/92282, respectively. A method for the treatment of hepatitis C infection (and flaviviruses and pestiviruses) in humans and other host animals is disclosed that includes administering an effective amount of a biologically active 1 ', 2', or 3 '-branched β-D or β-L nucleosides or a pharmaceutically acceptable salt or prodrug thereof, administered either alone or in combination, optionally in a pharmaceutically acceptable carrier.

WO 01/96353 to Indenix Pharmaceuticals, Ltd. discloses 3 '-prodrugs of 2'-deoxy-β-L-nucleosides for the treatment of HBV. U.S. Patent No. 4,957,924 to Beauchamp discloses various therapeutic esters of acyclovir.

Other patent applications disclosing the use of certain nucleoside analogs to treat hepatitis C virus include: PCT/CAOO/01316 (WO 01/32153) and PCTCA01/00197 (WO 01/60315) filed by BioChem Pharma, Inc. (now Shire Biochem, Inc.); PCT/US02/01531 (WO 02/057425 A2) and PCT/US02/03086 (WO 02/057287) filed by Merck & Co., Inc., and PCTEP01/09633 (WO 02/18404) filed by Hoffman La Roche.

In view of the severity of diseases associated with pestiviruses and flaviviruses, and their pervasiveness in animal and man, it is an object of the present invention to provide a compound, method and composition for the treatment of a host infected with flavivirus or pestivirus.

SUMMARY OF THE INVENTION

Compounds, methods and compositions for the treatment of a host infected with a flavivirus or pestivirus infection are described that includes an effective treatment amount of a β-D- or β-L-nucleoside of the Formulas (I) - (VI), or a pharmaceutically acceptable salt or prodrug thereof. In a first principal embodiment, a compound of Formula I, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

(I) wherein:

R¹, R² and R³ are independently H, phosphate (including mono-, di- or triphosphate and a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R , R or R³ is independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴;

X¹ and X² are independently selected from the group consisting of H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁵; and

R⁴ and R⁵ are independently hydrogen, acyl (including lower acyl), or alkyl (including but not limited to methyl, ethyl, propyl and cyclopropyl). In a second principal embodiment, a compound of Formula II, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

(II) wherein:

R , R and R are independently H, phosphate (including mono-, di- or triphosphate and a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴;

X¹ is selected from the group consisting of H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR^S; and

R⁴ and R⁵ are independently hydrogen, acyl (including lower acyl), or alkyl (including but not limited to methyl, ethyl, propyl and cyclopropyl). In a third principal embodiment, a compound selected from Formulas JJI, TV and V, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

(III) (IV) (V) wherein:

Base is a purine or pyrimidine base as defined herein;

R¹, R² and R³ are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br- vinyl, 2-Br-ethyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -Oøower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), CF_3j chloro, bromo, fluoro, iodo, NO , NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

In a fourth principal embodiment the invention provides a compound of Formula VI, or a pharmaceutically acceptable salt or prodrug thereof:

(VI) wherein:

Base is a purine or pyrimidine base as defined herein;

R and R² are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherem the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R² is independently H or phosphate;

R⁶ is hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br- vinyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), - O(lower alkyl), -O(alkenyl), chloro, bromo, fluoro, iodo, NO₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂;

R⁷ and R⁹ are independently hydrogen, OR², hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br-vinyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), chlorine, bromine, iodine, N0₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, - N(acyl)₂;

R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; alternatively, R⁷ and R⁹, R⁷ and R¹⁰, R⁸ and R⁹, or R⁸ and R¹⁰ can come together to form a pi bond; and

X is O, S, SO₂ or CH₂.

The β-D- and β-L-nucleosides of this invention may inhibit flavivirus or pestivirus polymerase activity. These nucleosides can be assessed for their ability to inhibit flavivirus or pestivirus polymerase activity in vitro according to standard screening methods.

In one embodiment the efficacy of the anti-flavivirus or pestivirus compound is measured according to the concentration of compound necessary to reduce the plaque number of the virus in vitro, according to methods set forth more particularly herein, by 50% (i.e. the compound's EC₅₀). In preferred embodiments the compound exhibits an EC₅₀ of less than 15 or preferably, less than 10 micromolar in vitro.

In another embodiment, the active compound can be administered in combination or alternation with another anti-flavivirus or pestivirus agent. In combination therapy, effective dosages of two or more agents are administered together, whereas during alternation therapy an effective dosage of each agent is administered serially. The dosages will depend on absorption, inactivation and excretion rates of the drug as well as other factors known to those of skill in the art. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be further understood that for any particular subject, specific dosage regimens and schedules should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions.

HCV is a member of the Flaviviridae family; however, now, HCV has been placed in a new monotypic genus, hepacivirus. Therefore, in one embodiment, the flavivirus or pestivirus is not HCV. Nonlimitmg examples of antiviral agents that can be used in combination with the compounds disclosed herein include:

(1) an interferon and/or ribavirin (Battaglia, A.M. et al, Ann. Pharmacother. 34:487-494, 2000); Berenguer, M. et al. Antivir. Ther. 3(Suppl. 3):125-136, 1998);

(2) Substrate-based NS3 protease inhibitors (Attwood et al, Antiviral peptide derivatives, PCT WO 98/22496, 1998; Attwood et al, Antiviral Chemistry and Chemotherapy 10.259-273, 1999; Attwood et al, Preparation and use of amino acid derivatives as anti-viral agents, German Patent Publication DE 19914474; Tung et al. Inhibitors of serine proteases, particularly hepatitis C virus NS3 protease, PCT WO 98/17679), including alphaketoamides and hydrazinoureas, and inhibitors that terminate in an electrophile such as a boronic acid or phosphonate. Llinas-Brunet et al, Hepatitis C inhibitor peptide analogues, PCT WO 99/07734.

(3) Non-substrate-based inhibitors such as 2,4,6-trihydroxy-3-nitro- benzamide derivatives(Sudo K. et al, Biochemical and Biophysical Research Communications, 238:643-647, 1997; Sudo K. et al. Antiviral Chemistry and Chemotherapy 9:186, 1998), including RD3-4082 and RD3-4078, the former substituted on the amide with a 14 carbon chain and the latter processing apara- phenoxyphenyl group;

(4) Thiazolidine derivatives which show relevant inhibition in a reverse- phase HPLC assay with an NS3/4A fusion protem and NS5A/5B substrate (Sudo K. et al, Antiviral Research 32:9-18, 1996), especially compound RD-1-6250, possessing a fused cinnamoyl moiety substituted with a long alkyl chain, RD4 6205 and RD4 6193;

(5) Thiazolidines and benzanilides identified in Kakiuchi N. et al. J. EBS Letters 421:217-220; Takeshita N. et al. Analytical Biochemistry 247:242-246, 1997; (6) A phenanthrenequinone possessing activity against protease in a SDS- PAGE and autoradiography assay isolated from the fermentation culture broth of Streptomyces sp., Sch 68631 (Chu M. et al, Tetrahedron Letters 3' ^?:7229-7232, 1996), and Sch 351633, isolated from the fungus Penicillium griscofuluum, which demonstrates activity in a scintillation proximity assay (Chu M. et al, Bioorganic andMedicinal Chemistry Letters 9:1949-1952);

(7) Selective NS3 inhibitors based on the macromolecule elgin c, isolated from leech (Qasim M.A. et al, Biochemistry 36:1598-1607, 1997);

(8) Helicase inhibitors (Diana G.D. et al, Compounds, compositions and methods for treatment of hepatitis C, U.S. Patent No. 5,633,358; Diana G.D. et al, Piperidine derivatives, pharmaceutical compositions thereof and their use in the treatment of hepatitis C, PCT WO 97/36554);

(9) Polymerase inhibitors such as nucleotide analogues, gliotoxin (Ferrari R. et al. Journal of Virology 73:1649-1654, 1999), and the natural product cerulenin (Lohmann V. et al, Virology 249:108-118, 1998);

(10) Antisense phosphorothioate oligodeoxynucleotides (S-ODN) complementary to sequence stretches in the 5' non-coding region (NCR) of the virus (Alt M. et al, Hepatology 22:707-717, 1995), or nucleotides 326-348 comprising the 3' end of the NCR and nucleotides 371-388 located in the core coding region of the IICV RNA (Alt M. et al, Archives of Virology 142:589-599, 1997; Galderisi U. et al, Journal of Cellular Physiology 181:251-257, 1999);

(11) Inhibitors of IRES-dependent translation (Ikeda N et al, Agent for the prevention and treatment of hepatitis C, Japanese Patent Publication JP- 08268890; Kai Y. et al Prevention and treatment of viral diseases, Japanese Patent Publication JP-10101591);

(12) Nuclease-resistant ribozymes. (Maccjak D.J. et al, Hepatology 30 abstract 995, 1999); and (13) Other miscellaneous compounds including 1-amino- alkylcyclohexanes (U.S. Patent No. 6,034,134 to Gold et al), alkyl lipids (U.S. Patent No. 5,922,757 to Chojkier et al), vitamin E and other antioxidants (U.S. Patent No. 5,922,757 to Chojkier et al), squalene, amantadine, bile acids (U.S. Patent No. 5,846,964 to Ozeki et al), N-(phosphonoaceιyl)-L-aspartic acid, (U.S. Patent No. 5,830,905 to Diana et al), benzenedicarboxamides (U.S. Patent No. 5,633,388 to Diana et al), polyadenylic acid derivatives (U.S. Patent No. 5,496,546 to Wang et al), 2',3'-dideoxyinosine (U.S. Patent No. 5,026,687 to Yarchoan et al), and benzimidazoles (U.S. Patent No. 5,891,874 to Colacino et al).

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 provides the structure of various non-limiting examples of nucleosides of the present invention, as well as other known nucleosides, FIAU and ribavirin, which are used as comparative examples in the text.

Figure 2 is a non-limiting illustration of the synthesis of a pentodialdo- furanose of the present invention, l-O-methyl-2,3-O-isopropylidene β-D-ribo- pentodialdo-furanose (2) and a 4 '-modified sugar of the present invention, 5-O- benzoyl-4-C-methyl- 1 ,2,3 -O-acetyl-α, β-D-ribofuranose (7) .

Figure 3 is a non-limiting illustration of the synthesis of various 4'- modified pyrimidine nucleoside of the present invention, including l-(4-C- methyl-β-D-ribofuranosyl)-uracil (9), 1 -(4-C-methyl-β-D-ribofuranosyl)4-thio- uracil (11) and l-(4-C-methyl-β-D-ribo-furanosyl)thymine (14); and pharmaceutically acceptable salts, including l-(4-C-methyl-β-D- ribofuranosyl)cytosine, hydrochloric form (12) and l-(4-C-methyl-β-D- ribofuranosyl)-5-methyl-cytosine, hydrochloride form (17). Figure 4 is a non-limiting illustration of the synthesis of a 4 '-modified purine nucleoside of the present invention, 9-(4-C-methyl-β-D-ribofuranosyl) guanine (19).

Figure 5 is a non-limiting illustration of the synthesis of a 4 '-modified purine nucleoside of the present invention, 9-(4-C-methyl-β-D-ribofuranosyl) adenine (21).

DETAILED DESCRIPTION OF THE INVENTION

The invention as disclosed herein is a compound, method and composition for the treatment of pestiviruses and flaviviruses in humans and other host animals, that includes the administration of an effective flavivirus or pestivirus treatment amount of a β-D- or β-L-nucleoside as described herein or a pharmaceutically acceptable salt or prodrug thereof, optionally in a pharmaceutically acceptable carrier. The compounds of this invention either possess antiviral (i.e., anti-flavivirus or pestivirus) activity, or are metabolized to a compound that exhibits such activity.

In summary, the present invention includes the following features:

(a) β-D- and β-L-nucleosides, as described herein, and pharmaceutically acceptable salts and prodrugs thereof;

(b) β-D- and β-L-nucleosides as described herein, and pharmaceutically acceptable salts and prodrugs thereof for use in the treatment or prophylaxis of a flavivirus or pestivirus infection, especially in individuals diagnosed as having a flavivirus or pestivirus infection or being at risk for becoming infected by flavivirus or pestivirus;

(c) use of these β-D- and β-L-nucleosides, and pharmaceutically acceptable salts and prodrugs thereof in the manufacture of a medicament for treatment of a flavivirus or pestivirus infection; (d) pharmaceutical formulations comprising the β-D- and β-L-nucleosides or pharmaceutically acceptable salts or prodrugs thereof together with a pharmaceutically acceptable carrier or diluent;

(e) β-D- and β-L-nucleosides as described herein substantially in the absence of enantiomers of the described nucleoside, or substantially isolated from other chemical entities;

(f) processes for the preparation of β-D- and β-L-nucleosides, as described in more detail below; and

(g) processes for the preparation of β-D- and β-L-nucleosides substantially in the absence of enantiomers of the described nucleoside, or substantially isolated from other chemical entities.

Flaviviruses included within the scope of this invention are discussed generally in Fields Virology, Editors: Fields, B. N., Knipe, D. M., and Howley, P. M., Lippincott-Raven Publishers, Philadelphia, PA, Chapter 31, 1996. Specific flaviviruses include, without limitation: Absettarov, Alfuy, Apoi, Aroa, Bagaza, Banzi, Bouboui, Bussuquara, Cacipacore, Carey Island, Dakar bat, Dengue 1, Dengue 2, Dengue 3, Dengue 4, Edge Hill, Entebbe bat, Gadgets Gully, Hanzalova, Hypr, Ilheus, Israel turkey meningoencephalitis, Japanese encephalitis, Jugra, Jutiapa, Kadam, Karshi, Kedougou, Kokobera, Koutango, Kumlinge, Kunjin, Kyasanur Forest disease, Langat, Louping ill, Meaban, Modoc, Montana myotis leukoencephalitis, Murray valley encephalitis, Naranjal, Negishi, Ntaya, Omsk hemorrhagic fever, Phnom-Penh bat, Powassan, Rio Bravo, Rocio, Royal Farm, Russian spring-summer encephalitis, Saboya, St. Louis encephalitis, Sal Vieja, San Perlita, Saumarez Reef, Sepik, Sokuluk, Spondweni, Stratford, Tembusu, Tyuleniy, Uganda S, Usutu, Wesselsbron, West Nile, Yaounde, Yellow fever, and Zika.

Pestiviruses included within the scope of this invention are discussed generally in Fields Virology, Editors: Fields, B. N., Knipe, D. M., and Howley, P. M., Lippincott-Raven Publishers, Philadelphia, PA, Chapter 33, 1996. Specific pestiviruses include, without limitation: bovine viral diarrhea virus ("BVDV"), classical swine fever virus ("CSFV," also called hog cholera virus), and border disease virus ("BDV").

I. Active Compound, and Physiologically Acceptable Salts and Prodrugs Thereof

In a first principal embodiment, a compound of Formula I, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

(I) wherein:

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X and X are independently selected from the group consisting of H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NE^NR⁵ or SR⁵; and

R⁴ and R⁵ are independently hydrogen, acyl (including lower acyl), or alkyl (including but not limited to methyl, ethyl, propyl and cyclopropyl).

In a preferred subembodiment, a compound of Formula I, or a pharmaceutically acceptable salt or prodrug thereof, is provided wherein:

R¹, R² and R³ are independently H or phosphate (preferably H);

X^I is H; X² is H orNH₂; and

Y is hydrogen, bromo, chloro, fluoro, iodo, NH₂ or OH.

In a second principal embodiment, a compound of Formula II, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

(II) wherein:

R¹, R² and R³ are independently H, phosphate (including mono-, di- or triphosphate and a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including' methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴;

X¹ is selected from the group consisting of H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ orSR⁵; and

In a preferred subembodiment, a compound of Formula II, or a pharmaceutically acceptable salt or prodrug thereof, is provided wherein:

R¹, R² and R³ are independently H or phosphate (preferably H);

X¹ is H or CH₃; and

Y is hydrogen, bromo, chloro, fluoro, iodo, NH₂ or OH.

In a third principal embodiment, a compound selected from Formulas III, IV and V, or a pharmaceutically acceptable salt or prodrug thereof, is provided:

wherein: Base is a purine or pyrimidine base as defined herein;

R , R and R are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br- vinyl, 2-Br-ethyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), CF₃, chloro, bromo, fluoro, iodo, NO₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

In a first preferred subembodiment, a compound of Formula III, IV or V, or a pharmaceutically acceptable salt or prodrug thereof, is provided wherein:

Base is a purine or pyrimidine base as defined herein;

R¹, R² and R³ are independently hydrogen or phosphate;

R⁶ is alkyl; and

X is O, S, SO₂ or CH₂.

In a second preferred subembodiment, a compound of Formula III, IV or V, or a pharmaceutically acceptable salt or prodrug thereof, is provided wherein:

Base is a purine or pyrimidine base as defined herein;

R¹, R² and R³ are hydrogens;

R⁶ is alkyl; and X is O, S, SO₂ or CH₂.

In a third preferred subembodiment, a compound of Formula III, IV or V, or a pharmaceutically acceptable salt or prodrug thereof, is provided wherein:

Base is a purine or pyrimidine base as defmed herein;

R¹, R² and R³ are independently hydrogen or phosphate;

R⁶ is alkyl; and

X is O.

In even more preferred subembodiments, a compound of Formula IV, or its pharmaceutically acceptable salt or prodrug, is provided:

(IN) wherem:

Base is a purine or pyrimidine base as defined herein; optionally substituted with an amine or cyclopropyl (e.g., 2-amino, 2,6-diamino or cyclopropyl guanosine); and

R¹ and R² are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R² is independently H or phosphate. In a fourth principal embodiment the invention provides a compound of Formula VI, or a pharmaceutically acceptable salt or prodrug thereof:

(VI) wherein:

Base is a purine or pyrimidine base as defined herein;

R¹ and R² are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R² is independently H or phosphate;

R is hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br- vinyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), - O(lower alkyl), -O(alkenyl), chloro, bromo, fluoro, iodo, NO₂₎ NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂;

R⁷ and R⁹ are independently hydrogen, OR², hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br-vinyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(Iower alkyl), -O(alkenyl), chlorine, bromine, , iodine, NO₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, - N(acyl)₂; i n

R and R are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; alternatively, R⁷ and R⁹, R⁷ and R¹⁰, R⁸ and R⁹, or R⁸ and R¹⁰ can come together to form a pi bond; and

X is O, S, SO₂ or CH₂.

In a first preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR², alkyl, alkenyl, alkynyl, Br- vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine, or iodine; and (6) X is O, S, SO₂ or CH₂.

In a second preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl, alkenyl, alkynyl, Br-vinyl, hydroxy, O-alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino, or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR²; (5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine, or iodine; and (6) X is O, S, SO₂ or CH₂.

In a third preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when admimstered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl, alkenyl, alkynyl, Br-vinyl, hydroxy, O-alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR², alkyl, alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (5) R⁸ and R¹⁰ are H; and (6) X is O, S, SO₂ or CH₂.

In a fourth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate. ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherem the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl, alkenyl, alkynyl, Br-vinyl, hydroxy, O-alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino, or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR², alkyl, alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, N0₂, amino, loweralkylamino, or di(loweralkyl)amino;

(5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine, or iodine; and (6) X is O.

In a fifth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR¹; (5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; and

(6) X is O, S, SO₂ or CH₂.

In a sixth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR², alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino, or di(loweralkyl)amino; (5) R⁸ and R¹⁰ are H; and (6) X is O, S, SO₂, or CH₂.

In a seventh preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR², alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (5) R and R are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; and (6) X is O.

In a eighth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R^! is independently H or phosphate; (3) R⁶ is alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, hydroxy, O- alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR²; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O, S, SO₂ or CH₂.

In a ninth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, hydroxy, O- alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR²; (5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; and (6) X is O.

In a tenth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is independently H or phosphate; (3) R⁶ is alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, hydroxy, O- alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (4) R⁷ and R⁹ are independently OR², alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino, or di(loweralkyl)amino; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O.

In an eleventh preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R is independently H or phosphate; (3) R⁶ is alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, hydroxy, O-alkyl, O-alkenyl, chloro, bromo, fluoro, iodo, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (4) R and R are independently OR ; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O, S, SO₂ or CH₂.

In a twelfth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR²; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O, S, SO₂, or CH₂.

In a thirteenth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR²; (5) R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine, or iodine; and (6) X is O.

In a fourteenth preferred subembodiment, a compound of Formula VI, or its pharmaceutically acceptable salt or prodrug, is provided in which: (1) Base is a purine or pyrimidine base as defined herein; (2) R¹ is independently H or phosphate; (3) R⁶ is alkyl; (4) R⁷ and R⁹ are independently OR², alkyl (including lower alkyl), alkenyl, alkynyl, Br-vinyl, O-alkenyl, chlorine, bromine, iodine, NO₂, amino, loweralkylamino or di(loweralkyl)amino; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O.

In even more preferred subembodiments, a compound of Formula VL or its pharmaceutically acceptable salt or prodrug, is provided in which:

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is guanine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is cytosine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is thymine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is uracil; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is adenine; (2) R¹ is phosphate; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is ethyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O; (1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is propyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is butyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ is hydrogen and R⁹ is hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is O;

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is S;

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R¹⁰ are hydrogen; and (6) X is SO₂; or

(1) Base is adenine; (2) R¹ is hydrogen; (3) R⁶ is methyl; (4) R⁷ and R⁹ are hydroxyl; (5) R⁸ and R^!0 are hydrogen; and (6) X is CH₂.

The β-D- and β-L-nucleosides of this invention may inhibit flavivirus or pestivirus polymerase activity. Nucleosides can be screened for their ability to inhibit flavivirus or pestivirus polymerase activity in vitro according to screening methods set forth more particularly herein. One can readily determine the spectrum of activity by evaluating the compound in the assays described herein or with another confirmatory assay.

In one embodiment the efficacy of the anti-flavivirus or pestivirus compound is measured according to the concentration of compound necessary to reduce the plaque number of the virus in vitro, according to methods set forth more particularly herein, by 50% (i.e. the compound's EC₅₀). In preferred embodiments the compound exhibits an EC₅₀ of less than 15 or 10 micromolar.

HCV is a member of the Flaviviridae family; however, now, HCV has been placed in a new monotypic genus, hepacivirus. Therefore, in one embodiment, the flavivirus or pestivirus is not HCV. The active compound can be administered as any salt or prodrug that upon administration to the recipient is capable of providing directly or indirectly the parent compound, or that exhibits activity itself. Nonlimiting examples are the pharmaceutically acceptable salts (alternatively referred to as "physiologically acceptable salts"), and a compound, which has been alkylated or acylated at the 5 '-position, or on the purine or pyrimidine base (a type of "pharmaceutically acceptable prodrug"). Further, the modifications can affect the biological activity of the compound, in some cases increasing the activity over the parent compound. This can easily be assessed by preparing the salt or prodrug and testing its antiviral activity according to the methods described herein, or other methods known to those skilled in the art.

II. Definitions

The term alkyl, as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic, primary, secondary, or tertiary hydrocarbon of typically to o, and specifically includes methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, cyclohexylmethyl, 3- methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl. The term includes both substituted and unsubstituted alkyl groups. Moieties with which the alkyl group can be substituted are selected from the group consisting of hydroxyl, halo (including independently F, CI, Br, and I), amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, carboxamido, carboxylate, thio, alkylthio, azido, sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate, either unprotected, or protected as necessary, as known to those skilled in the art, for example, as taught in Greene, et al, Protective Groups in Organic Synthesis. John Wiley and Sons, Second Edition, 1991, hereby incorporated by reference. In one embodiment, the alkyl can be , for example, CF₃, CH₂CF₃, CC1 , or cyclopropyl. In the text, whenever the term C(alkyl range) is used, the term independently includes each member of that class as if specifically and separately set out. The term lower alkyl, as used herein, and unless otherwise specified, refers to a Ci to C saturated straight, branched, or if appropriate, a cyclic (for example, cyclopropyl) alkyl group, including both substituted and unsubstituted forms. Unless otherwise specifically stated in this application, when alkyl is a suitable moiety, lower alkyl is preferred. Similarly, when alkyl or lower alkyl is a suitable moiety, unsubstituted alkyl or lower alkyl is preferred.

The term alkylamino or arylamino refers to an amino group that has one or two alkyl or aryl substituents, respectively.

The term "protected" as used herein and unless otherwise defined refers to a group that is added to an oxygen, nitrogen, or phosphorus atom to prevent its further reaction or for other purposes. A wide variety of oxygen and nitrogen protecting groups are known to those skilled in the art of organic synthesis.

The term aryl, as used herein, and unless otherwise specified, refers to phenyl, biphenyl, or naphthyl, and preferably phenyl. The term includes both substituted and unsubstituted moieties. The aryl group can be substituted with one or more moieties selected from the group consisting of alkyl, halo (independently F, CI, Br, or I), hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, carboxamido, carboxylate, thio, alkylthio, sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate, either unprotected, or protected as necessary, as known to those skilled in the art, for example, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991.

The term alkaryl or alkylaryl refers to an alkyl group with an aryl substituent. The term aralkyl or arylalkyl refers to an aryl group with an alkyl substituent.

The term halo, as used herein, includes chloro, bromo, iodo, and fluoro.

The term purine or pyrimidine base includes, but is not limited to, adenine, N -alkylpurines, N⁶-acylpurines (wherein acyl is C(O)(alkyl, aryl, alkylaryl, or arylalkyl), N -benzylpurine, N -halopurine, N -vinylpurine, N - acetylenic purine, N⁶-acyl purine, N⁶-hydroxyalkyl purine, N⁶-thioalkyl purine, N²-alkylpurines, N²-alkyl-6-thiopurines, thymine, cytosine, 5-fluorocytosine, 5- methylcytosine, 6-azapyrimidine, including 6-azacytosine, 2- and/or 4- mercaptopyrmidine, uracil, 5-halouracil, including 5-fluorouracil, C⁵- alkylpyrirnidines, C⁵-benzylpyrimidines, C⁵-halopyrimidines, C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine, C⁵- hydroxyalkyl purine, C⁵-amidopyrimidine, C⁵-cyanopyrimidine, C⁵- nitropyrimidine, C⁵-aminopyrimidine, N²-alkylpurines, N²-aIkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl, triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, pyrazolopyrimidinyl,

⁽0 (ϋ) (iii)

(iv) (v) (vi)

wherein A, G, and L are each independently CH or N; D is N, CH, C-CN, C-NO₂, C-Q_-3 alkyl, C-NHCONH₂, C-CONQ^uQ^π, C- CSNQ'O", CCOOQ¹¹, C-C(=NH)NH₂, C-hydroxy, C-Cι_-3alkoxy,C-amino, C-C_]-4 alkylamino, C-di(C_M alkyl)amino, C-halogen, C-(l,3-oxazol-2-yl), C-(l,3- thiazol-2-yl), or C-(imidazol-2-yl); wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and _-3 alkoxy; E is N or CQ⁵; is O, S, orNR;

R is H, OH, alkyl;

Q⁶ is H, OH, SH, NH₂, C_M alkylamino, di(C_!-4 alkyl)amino, C_3-6 cycloalkylamino, halogen,

C_M alkyl, C alkoxy, or CF₃;

Q⁵ is H, Cι-₆ alkyl, C_2-6 alkenyl, C_2-6 alkynyl, C_M alkylamino, CF , halogen, N, CN, NO₂, NHCONH₂, CONQ^πQⁿ, CSNQⁿQ^π, COOQ¹¹, C(=NH)NH₂, hydroxy, Cι_-3alkoxy,amino, C_M alkylamino, i(Cι-₄ alkyl)amino, halogen, l,3-oxazol-2-yl, l,3-thiazol-2-yl, or imidazol-2-yl; wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and _-3 alkoxy;

Q⁷ and Q¹⁴ are each independently selected from the group consisting of H, CF ,

OH, SH, OR, SR C_M alkyl, amino, C_M alkylamino, C _-6 cycloalkylamino, and di(C alkyl)amino;

Q¹¹ is independently H or C _{\ -6} alkyl;

Q⁸ is H, halogen, CN, carboxy, C alkyloxycarbonyl, N₃, amino, C_M alkylamino, di(CM alkyl)amino, hydroxy, Cι_-6 alkoxy, Q-β alkylthio, C alkylsulfonyl, (C_M alkyl)0-2 aminomethyl, N, CN, NO₂, C_M alkyl, NHCONH₂,

CONQⁿQⁿ, CSNQV, COOQ¹¹, C(=NH)NH₂, l,3-oxazol-2-yl, l,3-thiazol-2- yl, or imidazol-2-yl, wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and

Cι-3 alkoxy;

(D) (E)

wherein:

T] and T₂ are independently selected from N, CH, or C-Q¹⁶;

Q¹⁶,U, and Y are independently selected from is H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl, -O-alkyl, -O-alkenyl, -O- alkynyl, -O-aryl, -O-aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N-aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S- cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH_2j CO₂-alkyl, CONH-alkyl, CON- dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_mNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mNO₂, (CH₂)_mCONH₂, CM alkylamino, di(C_1-4 alkyl)amino, C_3-6 cycloalkylamino, C alkoxy, C alkoxycarbonyl, Cι_-6 alkylthio, Cι_₆ alkylsulfonyl, (C_]- alkyl)_0- a inomethyl, or-NHC(=NH)NH₂; R⁴ and R⁵ are independently selected from hydrogen, acyl (including lower acyl), or alkyl (including but not limited to methyl, ethyl, propyl and cyclopropyl);

m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;

Z is S, SO, SO₂, C=O, or Q .^:20.

Q ^■^20^u is H or alkyl; and

Vi and V₂ are independently selected from CH or N;

(F) (G) (H) (I) wherein:

T₃ and T₄ are independently selected from N or CQ .22.

Q²² is independently selected from H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl, -O-alkyl, -O-alkenyl, -O-alkynyl, -O-aryl, -O- aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N- aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S-cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH₂, CO₂-alkyl, CONH-alkyl, CON-dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_mNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mNO₂, (CH₂)_mCONH₂, C_1-4 alkylamino, di(C alkyl)amino, C_3-6 cycloalkylamino, C_M alkoxy, C_1- alkoxycarbonyl, Cι_-6 alkylthio, C_1-6 alkylsulfonyl, (CM alkyl)_0-2 aminomethyl, or -NHC(=NH)NH₂;

R⁴ and R⁵ are independently selected from hydrogen, acyl (including lower acyl), or alkyl (including but not limited to methyl, ethyl, propyl and cyclopropyl);

m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;

T₆, T₇, T₈, T₉, Tio, Tii, and T are independently selected from N or CH;

U₂ is H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵;

Y₂ is O, S, NH, NR or CQ²⁴Q²⁶ where R is H, OH, or alkyl;

Q²⁴ and Q²⁶ are independently selected from H, alkyl, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵;

Further examples of purine bases include, but are not limited to, guanine, adenine, hypoxanthine, 2,6-diaminopurine, and 6-chloropurine. Functional oxygen and nitrogen groups on the base can be protected as necessary or desired. Suitable protecting groups are well known to those skilled in the art, and include trimethylsilyl, dimethylhexylsilyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl, trityl, alkyl groups, and acyl groups such as acetyl and propionyl, methanesulfonyl, and p-toluenesulfonyl.

The term acyl refers to a carboxylic acid ester in which the non-carbonyl moiety of the ester group is selected from straight, branched, or cyclic alkyl or lower alkyl, optionally substituted amido, alkoxyalkyl including methoxymethyl, aralkyl including benzyl, aryloxyalkyl such as phenoxymethyl, aryl including phenyl optionally substituted with chloro, bromo, fluoro, iodo, Ci to C alkyl or Ci to C₄ alkoxy, sulfonate esters such as alkyl or aralkyl sulphonyl including methanesulfonyl, the mono, di or triphosphate ester, trityl or monomethoxytrityl, substituted benzyl, trialkylsilyl (e.g. dimethyl-t-butylsilyl) or diphenylmethylsilyl. Aryl groups in the esters optimally comprise a phenyl group. The term "lower acyl" refers to an acyl group in which the non-carbonyl moiety is a lower alkyl.

As used herein, the term "substantially free of or "substantially in the absence of refers to a nucleoside composition that includes at least 95% to 98 % by weight, and even more preferably 99% to 100% by weight, of the designated enantiomer of that nucleoside. In a preferred embodiment, in the methods and compounds of this invention, the compounds are substantially free of enantiomers.

Similarly, the term "isolated" refers to a nucleoside composition that includes at least 95% to 98 % by weight, and even more preferably 99% to 100% by weight, of the nucleoside, the remainder comprising other chemical species or enantiomers.

The term "independently" is used herein to indicate that the variable which is independently applied varies independently from application to application. Thus, in a compound such as R"XYR", wherein R" is "independently carbon or nitrogen," both R" can be carbon, both R" can be nitrogen, or one R" can be carbon and the other R" nitrogen.

The term host, as used herein, refers to an unicellular or multicellular organism in which the virus can replicate, including cell lines and animals, and preferably a human. Alternatively, the host can be carrying a part of the hepatitis C viral genome, whose replication or function can be altered by the compounds of the present invention. The term host specifically refers to infected cells, cells transfected with all or part of the HCV genome and animals, in particular, primates (including chimpanzees) and humans. In most animal applications of the present invention, the host is a human patient. Veterinary applications, in certain indications, however, are included in the present invention (such as chimpanzees).

The term "pharmaceutically acceptable salt or prodrug" is used throughout the specification to describe any pharmaceutically acceptable form (such as an ester, phosphate ester, salt of an ester or a related group) of a nucleoside compound which, upon administration to a patient, provides the nucleoside compound. Pharmaceutically acceptable salts include those derived from pharmaceutically acceptable inorganic or organic bases and acids. Suitable salts include those derived from alkali metals such as potassium and sodium, alkaline earth metals such as calcium and magnesium, among numerous other acids well known in the pharmaceutical art. Pharmaceutically acceptable prodrugs refer to a compound that is metabolized, for example hydrolyzed or oxidized, in the host to form the compound of the present invention. Typical examples of prodrugs include compounds that have biologically labile protecting groups on a functional moiety of the active compound. Prodrugs include compounds that can be oxidized, reduced, aminated, deaminated, hydroxylated, dehydroxylated, hydrolyzed, dehydrolyzed, alkylated, dealkylated, acylated, deacylated, phosphorylated, dephosphorylated to produce the active compound. The compounds of this invention possess antiviral activity against HCV, or are metabolized to a compound that exhibits such activity.

III. Nucleotide Salt or Prodrug Formulations

In cases where compounds are sufficiently basic or acidic to form stable nontoxic acid or base salts, administration of the compound as a pharmaceutically acceptable salt may be appropriate. Examples of pharmaceutically acceptable salts are organic acid addition salts formed with acids, which form a physiological acceptable anion, for example, tosylate, methanesulfonate, acetate, citrate, malonate, tartarate, succinate, benzoate, ascorbate, α-ketoglutarate, and α- glycerophosphate. , Suitable inorganic salts may also be formed, including, sulfate, nitrate, bicarbonate, and carbonate salts.

Pharmaceutically acceptable salts may be obtained using standard procedures well known in the art, for example by reacting a sufficiently basic compound such as an amine with a suitable acid affording a physiologically acceptable anion. Alkali metal (for example, sodium, potassium or lithium) or alkaline earth metal (for example calcium) salts of carboxylic acids can also be made.

Any of the nucleosides described herein can be administered as a nucleotide prodrug to increase the activity, bioavailability, stability or otherwise alter the properties of the nucleoside. A number of nucleotide prodrug ligands are known. In general, alkylation, acylation or other Hpophilic modification of the mono, di or triphosphate of the nucleoside will increase the stability of the nucleotide. Examples of substituent groups that can replace one or more hydrogens on the phosphate moiety are alkyl, aryl, steroids, carbohydrates, including sugars, 1,2-diacylglycerol and alcohols. Many are described in R. Jones and N. Bischofberger, Antiviral Research, 27 (1995) 1-17. Any of these can be used in combination with the disclosed nucleosides to achieve a desired effect.

The active nucleoside can also be provided as a 5'-phosphoether lipid or a 5 '-ether lipid, as disclosed in the following references, which are incorporated by reference herein: Kucera, L.S., N. Iyer, E. Leake, A. Raben, Modest E.K., D.L.W., and C. Piantadosi, "Novel membrane-interactive ether lipid analogs that inhibit infectious HIV-1 production and induce defective virus formation," AIDS Res. Hum. Retro Viruses, 1990, 6, 491-501; Piantadosi, C, J. Marasco C.J., S.L. Morris-Natschke, K.L. Meyer, F. Gumus, J.R. Surles, K.S. Ishaq, L.S. Kucera, N. Iyer, CA. Wallen, S. Piantadosi, and E.J. Modest, "Synthesis and evaluation of novel ether lipid nucleoside conjugates for anti-HIV activity," J. Med. Chem., 1991, 34, 1408-1414; Hosteller, K.Y., D.D. Richman, D.A. Carson, L.M. Stuhmiller, G.M. T. van Wijk, and H. van den Bosch, "Greatly enhanced inhibition of human immunodeficiency virus type 1 replication in CEM and HT4- 6C cells by 3'-deoxythymidine diphosphate dimyristoylglycerol, a lipid prodrug of 3,-deoxythymidine," Antimicrob. Agents Chemother., 1992, 36, 2025-2029; Hosetler, K.Y., L.M. Stuhmiller, H.B. Lenting, H. van den Bosch, and D.D. Richman, "Synthesis and antiretroviral activity of phospholipid analogs of azidothymidine and other antiviral nucleosides." J. Biol Chem., 1990, 265, 61127.

Nonlimiting examples of U.S. patents that disclose suitable Hpophilic substituents that can be covalently incorporated into the nucleoside, preferably at the 5'-OH position of the nucleoside or Hpophilic preparations, include U.S. Patent Nos. 5,149,794 (Sep. 22, 1992, Yatvin et al.); 5,194,654 (Mar. 16, 1993, Hostetler et al., 5,223,263 (June 29, 1993, Hostetler et al.); 5,256,641 (Oct. 26, 1993, Yatvin et al.); 5,411,947 (May 2, 1995, Hostetler et al.); 5,463,092 (Oct. 31, 1995, Hostetler et al.); 5,543,389 (Aug. 6, 1996, Yatvin et al.); 5,543,390 (Aug. 6, 1996, Yatvin et al.); 5,543,391 (Aug. 6, 1996, Yatvin et al.); and 5,554,728 (Sep. 10, 1996; Basava et al.), all of which are incorporated herein by reference. Foreign patent applications that disclose Hpophilic substituents that can be attached to the nucleosides of the present invention, or Hpophilic preparations, include WO 89/02733, W0 90/00555, W0 91/16920, WO 91/18914, W0 93/00910, W0 94/26273, W0 96/15132, EP 0 350 287, EP 93917054.4, and W0 91/19721.

IV. Combination and Alternation Therapy

It has been recognized that drug-resistant variants of viruses can emerge after prolonged treatment with an antiviral agent. Drug resistance most typically occurs by mutation of a gene that encodes for an enzyme used in viral replication. The efficacy of a drug against flavivirus or pestivirus infection can be prolonged, augmented, or restored by administering the compound in combination or alternation with a second, and perhaps third, antiviral compound that induces a different mutation from that caused by the principle drug. Alternatively, the pharmacokinetics, biodistribution or other parameter of the drug can be altered by such combination or alternation therapy. In general, combination therapy is typically preferred over alternation therapy because it induces multiple simultaneous stresses on the virus.

Any of the HCV treatments described in the Background of the Invention can be used in combination or alternation with the compounds described in this specification. Nonlimiting examples include:

(2) Substrate-based NS3 protease inhibitors (Attwood et al, Antiviral peptide derivatives, PCT WO 98/22496, 1998; Attwood et al, Antiviral Chemistry and Chemotherapy 10.259-273, 1999; Attwood et al, Preparation and use of amino acid derivatives as anti-viral agents, German Patent Publication DE 19914474; Tung et al Inhibitors of serine proteases, particularly hepatitis C virus NS3 protease, PCT WO 98/17679), including alphaketoamides and hydrazinoureas, and inhibitors that terminate in an electrophile such as a boronic acid or phosphonate. Llinas-Brunet et al, Hepatitis C inhibitor peptide analogues, PCT WO 99/07734.

(3) Non-substrate-based inhibitors such as 2,4₅6-trihydroxy-3-nitro- benzamide derivatives(Sudo K. et al, Biochemical and Biophysical Research Communications, 238:643-647, 1997; Sudo K. et al. Antiviral Chemistry and Chemotherapy 9:186, 1998), including RD3-4082 and RD3-4078, the former substituted on the amide with a 14 carbon chain and the latter processing apara- phenoxyphenyl group; (4) Thiazolidine derivatives which show relevant inhibition in a reverse- phase HPLC assay with an NS3/4A fusion protein and NS5A/5B substrate (Sudo K. et al, Antiviral Research 32:9-18, 1996), especially compound RD-1-6250, possessing a fused cinnamoyl moiety substituted with a long alkyl chain, RD4 6205 and RD4 6193;

(5) Thiazolidines and benzanilides identified in Kakiuchi N. et al. J. EBS Letters 421:217-220; Takeshita N. et al. Analytical Biochemistry 247:242-246, 1997;

(6) A phenanthrenequinone possessing activity against protease in a SDS- PAGE and autoradiography assay isolated from the fermentation culture broth of Streptomyces sp., Sch 68631 (Chu M. et al, Tetrahedron Letters 37:7229-7232, 1996), and Sch 351633, isolated from the fungus Penicϊllium griscofuluum, which demonstrates activity in a scintillation proximity assay (Chu M. et al, Bioorganic andMedicinal Chemistry Letters 9:1949-1952);

(7) Selective NS3 inhibitors based on the macromolecule elgin c, isolated from leech (Qasi M.A. et al, Biochemistry 36:1598-1607, 1997);

(9) Polymerase inhibitors such as nucleotide analogues, gliotoxin (Ferrari R. et al. Journal of Virology 73:1649-1654, 1999), and the natural product cerulenin (Lohmann V. et al, Virology 249: 108-118, 1998);

(10) Antisense phosphorothioate oligodeoxynucleotides (S-ODN) complementary to sequence stretches in the 5' non-coding region (NCR) of the virus (Alt M. et al, Hepatology 22:707-717, 1995), or nucleotides 326-348 comprising the 3' end of the NCR and nucleotides 371-388 located in the core coding region of the HCV RNA (Alt M. et al, Archives of Virology 142:589-599, 1997; Galderisi U. et al, Journal of Cellular Physiology 181:251-257, 1999);

(11) Inhibitors of IRES-dependent translation (Ikeda N et al, Agent for the prevention and treatment of hepatitis C, Japanese Patent Publication JP- 08268890; Kai Y. et al. Prevention and treatment of viral diseases, Japanese Patent Publication JP-10101591);

(12) Nuclease-resistant ribozymes. (Maccjak D.J. et al, Hepatology 30 abstract 995, 1999); and

(13) Other miscellaneous compounds including 1-amino- alkylcyclohexanes (U.S. Patent No. 6,034,134 to Gold et al), alkyl lipids (U.S Patent No. 5,922,757 to Chojkier et al), vitamin E and other antioxidants (U.S Patent No.¹ 5,922,757 to Chojkier et al), squalene, amanxadine, bile acids (U.S Patent No. 5,846,964 to Ozeki et al), N-(phosphonoacetyl)-L-aspartic acid, (U.S Patent No. 5,830,905 to Diana et al), benzenedicarboxamides (U.S. Patent No 5,633,388 to Diana et al), polyadenylic acid derivatives (U.S. Patent No 5,496,546 to Wang et al), 2',3'-dideoxyinosine (U.S. Patent No. 5,026,687 to Yarchoan et al), and benzimidazoles (U.S. Patent No. 5,891,874 to Colacino et al).

V. Pharmaceutical Compositions

Host, including humans, infected with a flavivirus or pestivirus, can be treated by administering to the patient an effective amount of the active compound or a pharmaceutically acceptable prodrug or salt thereof in the presence of a pharmaceutically acceptable carrier or diluent. The active materials can be administered by any appropriate route, for example, orally, parenterally, intravenously, intradermally, subcutaneously, or topically, in liquid or solid form.

A preferred dose of the compound for flavivirus or pestivirus infection will be in the range from about 1 to 50 mg/kg, preferably 1 to 20 mg/kg, of body weight per day, more generally 0.1 to about 100 mg per kilogram body weight of the recipient per day. The effective dosage range of the pharmaceutically acceptable salts and prodrugs can be calculated based on the weight of the parent nucleoside to be delivered. If the salt or prodrug exhibits activity in itself, the effective dosage can be estimated as above using the weight of the salt or prodrug, or by other means known to those skilled in the art.

The compound is conveniently administered in unit any suitable dosage form, including but not limited to one containing 7 to 3000 mg, preferably 70 to 1400 mg of active ingredient per unit dosage form. A oral dosage of 50-1000 mg is usually convenient.

Ideally the active ingredient should be administered to achieve peak plasma concentrations of the active compound of from about 0.2 to 70 μM, preferably about 1.0 to 10 μM. This may be achieved, for example, by the intravenous injection of a 0.1 to 5% solution of the active ingredient, optionally in saline, or administered as a bolus of the active ingredient.

The concentration of active compound in the drug composition will depend on absoφtion, inactivation and excretion rates of the drug as well as other factors known to those of skill in the art. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be further understood that for any particular subject, specific dosage regimens should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions, and that the concentration ranges set forth herein are exemplary only and are not intended to limit the scope or practice of the claimed composition. The active ingredient may be administered at once, or may be divided into a number of smaller doses to be administered at varying intervals of time.

A preferred mode of administration of the active compound is oral. Oral compositions will generally include an inert diluent or an edible carrier. They may be enclosed in gelatin capsules or compressed into tablets. For the purpose of oral therapeutic administration, the active compound can be incorporated with excipients and used in the form of tablets, troches or capsules. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition.

The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring. When the dosage unit form is a capsule, it can contain, in addition to material of the above type, a liquid carrier such as a fatty oil. In addition, dosage unit forms can contain various other materials which modify the physical form of the dosage unit, for example, coatings of sugar, shellac, or other enteric agents.

The compound can be administered as a component of an elixir, suspension, syrup, wafer, chewing gum or the like. A syrup may contain, in addition to the active compounds, sucrose as a sweetening agent and certain preservatives, dyes and colorings and flavors.

The compound or a pharmaceutically acceptable prodrug or salts thereof can also be mixed with other active materials that do not impair the desired action, or with materials that supplement the desired action, such as antibiotics, antifungals, anti-inflammatories, or other antivirals, including other nucleoside compounds. Solutions or suspensions used for parenteral, intradermal, subcutaneous, or topical application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. The parental preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.

If administered intravenously, preferred carriers are physiological saline or phosphate buffered saline (PBS).

In a preferred embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation.

Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) are also preferred as pharmaceutically acceptable carriers. These may be prepared according to methods known to those skilled in the art, for example, as described in U.S. Patent No. 4,522,811 (which is incorporated herein by reference in its entirety). For example, liposome formulations may be prepared by dissolving appropriate lipid(s) (such as stearoyl phosphatidyl ethanolamine, stearoyl phosphatidyl choline, arachadoyl phosphatidyl choline, and cholesterol) in an inorganic solvent that is then evaporated, leaving behind a thin film of dried lipid on the surface of the container. An aqueous solution of the active compound or its monophosphate, diphosphate, and/or triphosphate derivatives is then introduced into the container. The container is then swirled by hand to free lipid material from the sides of the container and to disperse lipid aggregates, thereby forming the liposomal suspension. VI. Processes for the Preparation of Active Compounds

The nucleosides of the present invention can be synthesized by any means known in the art. In particular, the synthesis of the present nucleosides can be achieved by either alkylating the appropriately modified sugar, followed by glycosylation or glycosylation followed by alkylation of the nucleoside, though preferably alkylating the appropriately modified sugar, followed by glycosylation. The following non-limiting embodiments illustrate some general methodology to obtain the nucleosides of the present invention.

General Synthesis of 4 '-C-Branched Nucleosides

4'-C-Branched ribonucleosides of the following structure:

wherein BASE is a purine or pyrimidine base as defined herein;

R⁷ and R⁹ are independently hydrogen, OR², hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br-vinyl, -C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), chlorine, bromine, iodine, NO₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, - N(acyl)₂;

R⁸ and R¹⁰ are independently H, alkyl (including lower alkyl), chlorine, bromine or iodine; alternatively, R⁷ and R⁹, R⁷ and R¹⁰, R⁸ and R⁹, or R⁸ and R¹⁰can come together to form a pi bond; R¹ and R² are independently H; phosphate (including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug); acyl (including lower acyl); alkyl (including lower alkyl); sulfonate ester including alkyl or arylalkyl sulfonyl including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted with one or more substituents as described in the definition of aryl given herein; a lipid, including a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherem R¹ is independently H or phosphate;

R⁶ is an alkyl, halogeno-alkyl (i.e. CF₃), alkenyl, or alkynyl (i.e. allyl); and

X is O, S, SO₂ or CH₂ can be prepared by the following general method.

Modification from the pentodialdo-furanose

The key starting material for this process is an appropriately substituted pentodialdo-furanose. The pentodialdo-furanose can be purchased or can be prepared by any known means including standard epimerization, substitution and cyclization techniques.

In a preferred embodiment, the pentodialdo-furanose is prepared from the appropriately substituted hexose. The hexose can be purchased or can be prepared by any known means including standard epimerization (e.g. via alkaline treatment), substitution and coupling techniques. The hexose can be either in the furanose form, or cyclized via any means known in the art, such as methodology taught by Townsend Chemistry of Nucleosides and Nucleotides, Plenum Press, 1994, preferably by selectively protecting the hexose, to give the appropriate hexafuranose.

The 4'-hydroxymethylene of the hexafuranose then can be oxidized with the appropriate oxidizing agent in a compatible solvent at a suitable temperature to yield the 4'-aldo-modified sugar. Possible oxidizing agents are Swern reagents, Jones reagent (a mixture of chromic acid and sulfuric acid), Collins's reagent (dipyridine Cr(VI) oxide, Corey's reagent (pyridinium chlorochromate), pyridinium dichromate, acid dichromate, potassium permanganate, MnO₂, ruthenium tetroxide, phase transfer catalysts such as chromic acid or permanganate supported on a polymer, Cl₂-pyridine, H₂O₂-ammonium molybdate, NaBrO₂-CAN, NaOCl in HOAc, copper chromite, copper oxide, Raney nickel, palladium acetate, Meerwin-Pondorf-Verley reagent (aluminum t- butoxide with another ketone) and N-bromosuccinimide, though preferably using H₃PO , DMSO and DCC in a mixture of benzene/pyridme at room temperature.

Then, the pentodialdo-furanose can be optionally protected with a suitable protecting group, preferably with an acyl or silyl group, by methods well known to those skilled in the art, as taught by Greene et al. Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. In the presence of a base, such as sodium hydroxide, the protected pentodialdo-furanose can then be coupled with a suitable electrophilic alkyl, halogeno-alkyl (i.e. CF₃), alkenyl or alkynyl (i.e. allyl), to obtain the 4'-alkylated sugar. Alternatively, the protected pentodialdo-furanose can be coupled with the corresponding carbonyl, such as formaldehyde, in the presence of a base, such as sodium hydroxide, with the appropriate polar solvent, such as dioxane, at a suitable temperature, which can then be reduced with an appropriate reducing agent to give the 4'-alkylated sugar. In one embodiment, the reduction is carried out using PhOC(S)Cl, DMAP, preferably in acetonitrile at room temperature, followed by treatment of ACCΝ and TMSS refluxed in toluene.

The optionally activated sugar can then be coupled to the BASE by methods well known to those skilled in the art, as taught by Townsend Chemistry of Nucleosides and Nucleotides. Plenum Press, 1994. For example, an acylated sugar can be coupled to a silylated base with a lewis acid, such as tin tetrachloride, titanium tetrachloride or trimethylsilyltriflate in the appropriate solvent at a suitable temperature. Subsequently, the nucleoside can be deprotected by methods well known to those skilled in the art, as taught by Greene et al. Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991.

In a particular embodiment, the 4'-C-branched ribonucleoside is desired. Alternatively, deoxyribo-nucleoside is desired. To obtain these deoxyribo- nucleosides, a formed ribo-nucleoside can optionally be protected by methods well known to those skilled in the art, as taught by Greene et al. Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991, and then the 2'-OH can be reduced with a suitable reducing agent. Optionally, the 2'- hydroxyl can be activated to facilitate reduction; i.e. via the Barton reduction.

In another embodiment of the invention, the L-enantiomers are desired. Therefore, the L-enantiomers can be corresponding to the compounds of the invention can be prepared following the same foregoing general methods, beginning with the corresponding L-pentodialdo-furanose as starting material.

The present invention is described by way of illustration, in the following examples. It will be understood by one of ordinary skill in the art that these examples are in no way limiting and that variations of detail can be made without departing from the spirit and scope of the present invention.

EXAMPLES

Melting points were determined in open capillary tubes on a Bϋchi B-545 apparatus and are uncorrected. The UV absorption spectra were recorded on an Uvikon XS spectrophotometer (99-9089). Η-NMR spectra were run at room temperature in DMSO-d₆ or CDC1₃ with a Bruker AC 200, 250 or 400 spectrometer. Chemical shifts are given in ppm, DMSO-d₆ or CDC1₃ being set at 2.49 or 7.26 ppm as reference. Deuterium exchange, decoupling experiments or 2D-COSY spectra were performed in order to confirm proton assignments. Signal multiplicities are represented by s (singlet), d (doublet), dd (doublet of doublets), t (triplet), q (quadruplet), br (broad), m (multiplet). All J-values are in Hz. FAB mass spectra were recorded in the positive - (FAB>0) or negative - (FAB>0) ion mode on a JEOL JMS DX 300 mass spectrometer; the matrix was a mixture (50:50, v/v) of glycerol and thioglycerol (GT). Thin layer chromatography was performed on precoated aluminum sheets of Silica Gel 60 F₂₅₄ (Merck, Art. 5554), visualization of products being accomplished by UV absorbency followed by charring with 10% ethanolic sulfuric acid and heating. Column chromatography was carried out on Silica Gel 60 (Merck, Art. 9385) at atmospheric pressure.

Example 1

Preparation ofl-O-Methyl-2, 3-O-isopropylidene-β-D-ribofuranose (1)

The title compound can be prepared according to a published procedure (Leonard, N. J.; Carraway, K. L. "5-Amino-5-deoxyribose derivatives. Synthesis and use in the preparation of "reversed" nucleosides" J. Heterocycl. Chem. 1966, 3, 485-489).

A solution of 50.0 g (0.34 mole) of dry D-ribose in 1.0 L of acetone, 100 mL of 2,2-dimethoxypropane, 200 mL of methanol containing 20 mL of methanol saturated with hydrogen chloride at 0°C was stirred overnight at room temperature. The resulting solution was neutralized with pyridine and evaporated under reduced pressure. The resulting oil was partitioned between 400 mL of water and 400 mL of methylene chloride. The water layer was extracted twice with methylene chloride (400 mL). The combined organic extracts were dried over sodium sulfate and evaporated under reduced pressure. The residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (1-2%) in methylene chloride] to give pure 1 (52.1 g, 75%) as a yellow syrup. ^]H-NMR (CDC1₃): δ 5.00 (s, IH, H-l), 4.86 (d, IH, H-2, J_2-3 = 5.9 Hz), 4.61 (d, IH, H-3, J_3-2 = 5.9 Hz), 4.46 (t, IH, H-4, J_4-5 = 2.7 Hz), 3.77-3.61 (m, 2H, H-5 and H-5'), 3.46 (s, IH, OCH₃), 3.0-2.4 (br s, IH, OH-5), 1.51 (s, 3H CH₃), 1.34 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 173 (M-OCH3)⁺.

Example 2

Preparation of l-O-Methyl-2, 3-O-isopropylidene-β-D-pentodialdo-ribofuranose

01

The title compound can be prepared according to a published procedure (Jones, G. H.; Moffatt, J. G. Oxidation of carbohydrates by the sulfoxide- carbodiimide and related methods. Oxidation with dicyclohexylcarbodiimide- DMSO, diisopropylcarbodiimide-DMSO, acetic anhydride-DMSO, and phosphorus pentoxide-DMSO: in Methods in Carbohydrate Chemistry; Whisler, R. L. and Moffatt, J. L. Eds; Academic Press: New York, 1972; 315-322).

Compound 1 was co-evaporated twice with anhydrous pyridine. Dicyclohexylcarbodi-imide (DCC, 137.8 g, 0.67 mol) was added to a solution of 1 (68.2 g, 0.33 mole) in anhydrous benzene (670 mL), DMSO (500 mL) and pyridine (13.4 mL). To the resulting solution, cooled to 0°C, was added a solution of anhydrous crystalline orthophosphoric acid (16.4 g, 0.167 mmol) in anhydrous DMSO (30 mL). The mixture was stirred for 1.5 hours at 0°C and 18 hours at room temperature under argon atmosphere, diluted with ethyl acetate (1000 mL). A solution of oxalic acid dihydrate (63.1 g, 038 mol) in DMSO (30 mL) was added and the reaction mixture was stirred at room temperature during 1 hour and then filtered to eliminate precipitated dicyclohexylurea (DCU). The filtrate was concentrated to a volume of about 600 mL under reduced pressure and neutralized with a saturated aqueous sodium hydrogen carbonate solution (400 mL). Brine (200 L) was added and the organic layer was extracted with ethyl acetate (4x 1000 L). The combined organic layers were concentrated to a volume of about 2000 mL, washed with a saturated aqueous sodium hydrogen carbonate solution (2x 700 mL), and with brine (2x 700 mL) before being dried over sodium sulfate and evaporated under reduced pressure. A small fraction of the crude residue was purified on silica gel chromatography [eluent: chloroform/ethyl ether, 8:2] in order to confirm the structure of 2 which was obtained as a pale yellow solid. 1H-NMR (CDC1₃): δ 9.61 (s, IH, H-5), 5.12 (s, IH, H-l), 5.08 (d, IH, H-2, J_2-3 = 5.9 Hz), 4.53 (d, IH, H-3, J_3-2 = 6.0 Hz), 4.51 (s, IH, H-4), 3.48 (s, IH, OCH₃), 1.56 (s, 3H CH₃), 1.36 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 203 (M+H)⁺, 171 (M-OCH₃)⁺.

Example 3

Preparation of 4-C-Hvdroxymethyl-l-0-methyl-2, -O-isopropylidene- β-D- ribofuranose (3)

The title compound can be prepared according to a published procedure (Leland, D. L.; Kotick, M. P. "Studies on 4-C-(hydroxymethyl)pentofuranoses. Synthesis of 9- [4-C-(hydroxymethyl)-a-L-tlιreo-pentofuranosyl] adenine" Carbohvdr. Res. 1974, 35, C9-C11; Jones, G. H.; Taniguchi, M.; Tegg, D.; Moffatt, J. G. "4'-substituted nucleosides. 5. Hydroxylation of nucleoside 5'- aldehydes" J. Ore. Chem. 1979, 44, 1309-1317; Gunic, E.; Girardet, J.-L.; Pietrzkowski, Z.; Esler, C; Wang, G. "Synthesis and cytotoxicity of 4'-C-and 5'- C-substituted Toyocamycins" Bioorg. Med. Chem. 2001, 9, 163-170).

To a solution of the crude material (2) obtained above and 37% aqueous formaldehyde (167 mL) in dioxane (830 mL) was added aqueous sodium hydroxyde (2N, 300 L). The mixture was stirred at room temperature for 4 hours and neutralized by addition of Dowex 50 W X 2 (H⁺ form). The resin was filtered, washed with methanol, and the combined filtrates were concentrated to dryness and coevaporated several times with absolute ethanol. Sodium formate which was precipitated from absolute ethanol was removed by filtration, the filtrate was concentrated to dryness and the residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (0-4%) in chloroform] to give pure 3 (42.2 g, 54%) from 1), which was recrystallized from cyclohexane. , Mp = 94-95 (dec.) (lit.94-96.5; 97-98 : Refs :3,4), Η-NMR (DMSO-de): δ 4.65 (s, IH, H-l), 4.44-4.37 (m, 3H, H-2, H-3 and OH-6), 4.27 (t, IH, OH-5, J = 5.6 Hz, J = 6.0 Hz), 3.42-3.34 (m, 2H, H-5 and H-6) 3.29 (dd, IH, H-5', J₅.-OH = 5.4 Hz, J5-5' = 11.4 Hz), 3.11 (dd, IH, H-6', J₆>_-0H = 5.7 Hz, J6-6' = 10.9 Hz), 3.03 (s, 3H, OCH₃), 1.48 (s, 3H CH₃), 1.05 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 469 (2M+H)⁺, 235 (M+H)⁺, 203 (M-OCH₃)+ FAB<0 m/z 233 (M-H)-.

Example 4

Preparation of 6-0-Morιornethoxytrityl-4-C-hydroxymethyl-l-0-methyl-2.3-0- isopropylidene-β-D-ribofuranose (4)

The title compound can be prepared according to a published procedure (Gunic, E.; Girardet, J.-L.; Pietrzkowski, Z.; Esler, C; Wang, G. "Synthesis and cytotoxicity of 4'-C-and 5'-C-substituted Toyocamycins" Bioorg. Med. Chem. 2001, 9, 163-170).

To a solution of 3 (41.0 g, 175 mmol) in pyridine (700 ml) was added by portions dimethoxytrityl chloride (60.5 g, 178 mmol) at +4°C. The reaction mixture was stirred for 3 hours at room temperature. After addition of methanol, the reaction mixture was concentrated (200 ml) and then dissolved with ethyl acetate (2 L). The organic layer was washed with a 5% aqueous sodium hydrogen carbonate solution, with water and dried over sodium sulfate and then evaporated to dryness. Purification by silica gel column chromatography [eluent: ethyl acetate / hexane 15/85] afforded pure 4 (63.0 g, 68%) as a syrup. ^!H-NMR (CDCI3): δ 7.5-6.9 (m, 13H, MMTr), 4.89 (s, IH, H-l), 4.72-4.62 (m, 3H, H-2, H-3 and OH-5), 3.82 (dd, IH, H-5, J_5-0H = 5.5 Hz, J5-5' = 10.5 Hz), 3.79 (s, 6H, OCH3), 3.54 (dd, IH, H-5', J₅.-OH = 4.9 Hz, J_{5 S} = 10.5 Hz), 3.31 (s, 3H, OCH₃), 3.24 (d, IH, H-6, J_M. = 9.2 Hz), 3.13 (d, IH, H-6', J₆'_-6 = 9.2 Hz), 1.24 (s, 3H CH₃), 1.15 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 303 (DMTr)⁺.

Example 5

Preparation gf_ 5-0-Benzoyl-4-C-hydroxymethyl-l-0-methyl-2,3-0- isopropylidene-β-D-ribo-furanose (5)

To a solution of 4 (2.51 g, 4.68 mmol) in anhydrous pyridine (37 mL) was added under argon benzoyl chloride (1.09 mL, 9.36 mmol) and the reaction mixture was stirred for 13 hours at to room temperature. Then the reaction was cooled to 0°C and stopped with ice-cold water (100 mL). The water layer was extracted with methylene chloride (3D 200 mL). The combined organic layers were washed with a saturated aqueous sodium hydrogen carbonate solution (2x 150 mL), with water (lx 150 mL) and then dried over sodium sulfate and evaporated under reduced pressure. The residue was dissolved in 80% acetic acid (70.2 mL) and the mixture was stirred at room temperature for 3hr and concentrated to dryness. Purification by silica gel column chromatography [eluent: chloroform] afforded pure 5 (1.40 g, 88%) as a syrup. 1H-NMR (CDCI₃): δ 8.1-7.4 (m, 5H, C₆H₅CO), 5.08 (s, IH, H-l), 4.77 (dd, 2H, H-2 and H- 3, J = 6.1 Hz, J = 8.2 Hz), 4.51 (q, 2H, H-5 and H-5', J = 11.5 Hz, J_5-5. = 23.8 Hz), 3.91 (t, 2H, H-6 and H-6', J = 12.3 Hz), 4.38 (s, IH, OCH₃), 2.2-1.8 (brs, IH, OH-6), 1.57 (s, 3H CH₃), 1.38 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 677 (2M+H)⁺, 339 (M+H)⁺, 307 (M-OCH₃)⁺, 105 (C₆H₅CO)⁺ FAB<0 m/z 121 (C₆H₅CO₂)-.

Example 6

Preparation of 5-Q-Benzoyl-4-C-methyl-l-0-methyl-2, 3-O-isopropylidene-β-D- ribofuranose (6)

A solution of 5 (37.6 g, 0.111 mol), 4-dimethylaminopyridine (DMAP,

40.7 g, 0.333 mol) and phenoxythiocarbonyle chloride in anhydrous acetonitrile (1000 mL) was stirred at room temperature for 1 hour and concentrated to dryness. The residue was dissolved in methylene chloride (500 mL) and successively washed with 0.2 M hydrochloric acid (2x 500 mL) and water (500 mL) before being dried over sodium sulfate, evaporated under reduced pressure and coevaporated several times with anhydrous toluene. The crude material was dissolved in anhydrous toluene (880 mL) and tris(trimethylsilyl)silane (TMSS, 42.9 mL, 0.139 mol), and l, -azobis(cyclohexanecarbonitrile) (ACCN, 6.8 g,

27.8 mmol) were added. The reaction mixture was stirred under reflux for 45 minutes, cooled to room temperature and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography [eluent: stepwise gradient of diethyl ether (5-20%) in petroleum ether] to give pure 6 (26.4 g, 74%) as a pale yellow syrup. Η-NMR (DMSO-d₆): δ 8.0-7.5 (m, 5H, C₆H₅CO), 4.85 (s, IH, H-l), 4.63 (dd, 2H, H-2 and H-3, J = 6.1 Hz, J = 11.6 Hz), 4.24 (d, IH, H-5, J_5-5- = 11.1 Hz), 4.10 (d, IH, H-5', -s = 11.1 Hz), 3.17 (s, IH, OCH₃), 1.38 (s, 3H CH₃), 1.30 (s, 3H CH₃), 1.25 (s, 3H CH₃); MS (matrix GT): FAB>0 m/z 291 (M-OCH₃)⁺, 105 (C₆H₅CO)⁺ FAB<0 m/z 121 (C₆H₅CO₂)^".

Example 7

Preparation of 5-0-Benzoyl-4-C-methyl-l ,2,3-0-acetyl-a, β-D-ribofuranose (7)

Compound 6 (22.5 g, 70 mmol) was suspended in a 80% aqueous acetic acid solution (250 mL). The solution was heated at 100°C for 3 hours. The volume was then reduced by half and coevaporated with absolute ethanol and pyridine. The oily residue was dissolved in pyridine (280 mL) and then cooled at 0°C. Acetic anhydride (80 mL) and 4-dimethylamino-pyridine (500 mg) were added. The reaction mixture was stirred at room temperature for 3 hours and then concentrated under reduced pressure. The residue was dissolved with ethyl acetate (1 L) and successively washed with a saturated aqueous sodium hydrogen carbonate solution, a 1 M hydrochloric acid and water. The organic layer was dried over sodium sulfate and evaporated under reduced pressure. The resulting residue was purified by silica gel column chromatography [eluent: stepwise gradient of diethyl ether (30-40%) in petroleum ether] to give pure 7 (16.2 g, 60%) as a pale yellow syrup. A small fraction of the material was re-purified on silica gel chromatography [same eluent: system] in order separate the α and the β anomers. α anomer: Η-NMR (DMSO-d₆): δ 8.1-7.5 (m, 5H, C₆H₅CO), 6.34 (pt, IH, H-l, J = 2.4 Hz, J = 2,1 Hz), 5.49 (m, 2H, H-2 and H-3), 4.33 (q, 2H, H-5 and H-5', J = 11.6 Hz, J = 18.7 Hz), 2.15 (s, 3H, CH₃CO₂), 2.11 (s, 3H, CH₃CO₂), 2.07 (s, 3H, CH₃CO₂), 1.37 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 335 (M-CH₃CO₂ ⁺, 275 (M-CH₃CO₂ ^"+H)⁺,105 (C₆H_sCO)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 111 (C₆H₅CO₂)-, 59 (CH₃CO₂)-. β anomer: Η-NMR (DMSO-d₆): δ 8.1-7.5 (m, 5H, C₆H₅CO), 5.99 (s, IH, H-l), 5.46 (d, IH, H-2, J_2-3 = 5.3 HZ), 5.30 (d, IH, H-2, J_2-3 = 5.3 Hz), 4.39 (d, IH, H- 5, J_5-5> = 11.7 Hz), 4.19 (d, IH, H-5', J₅>_-5 = 11.7 Hz), 2.10 (s, 3H, CH₃CO₂), 2.06 (s, 3H, CH₃CO₂), 2.02 (s, 3H, CH₃C0₂), 1.30 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z θ35 (M-CH₃CO₂ ^")⁺, 275 (M-CH₃CO₂ ^"+H)⁺,105 (C₆H₅CO)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 111 (C₆H₅CO₂)^", 59 (CH₃CO₂)^".

Example 8

Preparation of l-(5-0-Benzoyl-4-C-methyl-2,3-0-acetyl-β-D- ribofuranosvDuracil (8)

A suspension of uracil (422 mg, 3.76 mmol) was treated with hexamethyldisilazane (HMDS, 21 mL) and a catalytic amount of ammonium sulfate during 17 hours under reflux. After cooling to room temperature, the mixture was evaporated under reduced pressure, and the residue, obtained as a colorless oil, was diluted with anhydrous 1,2-dichloroethane (7.5 mL). To the resulting solution was added 7 (0.99 g, 2.51 mmol) in anhydrous 1,2- dichloroethane (14 mL), followed by addition of trimethylsilyl trifluoromethanesulfonate (TMSTf, 0.97 mL, 5.02 mmol). The solution was stirred for 2.5 hours at room temperature under argon atmosphere, then diluted with chloroform (150 mL), washed with the same volume of a saturated aqueous sodium hydrogen carbonate solution and finally with water (2x 100 mL). The organic phase was dried over sodium sulfate, then evaporated under reduced pressure. The resulting crude material was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (0-2%) in chloroform] to afford pure 8 (1.07 g, 95%) as a foam. Η-NMR (DMSO-d6): δ 11.48 (s, IH, NH), 8.1-7.5 ( , 6H, C₆H₅CO and H-6), 5.94 (d, IH, H-l', J_r.₂' = 3.3 Hz), 5.61 (m, 3H, H-5, H-2' and H-3'), 4.47 (d, IH, H-5', J_{5 5} ^„ = 11.7 Hz), 4.35 (d, IH, H- 5", J₅»_-5* = 11.7 Hz), 2.12 (s, 3H, CH₃CO₂), 2.09 (s, 3H, CH₃CO₂), 1.38 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 893 (2M+H)⁺, 447 (M+H)⁺, 335 (S)⁺, 113 (BH₂)⁺, 105 (C₆H₅CO)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 891 (2M-H)^", 445 (M-H)^", 121 (C₆H₅CO₂)-, 111 (B)\ 59 (CH₃CO₂)^".

Example 9

Preparation ofl-(4-C-methyl-β-D-ribofuranosyl)uracil (9)

The title compound can be prepared according to a published procedure from 8 (Waga, T.; Nishizaki, T.; Miyakawa, I.; Orhui, H.; Meguro, H. "Synthesis of 4'-C-methvlnucleosides" Biosci. Biotechnol. Biochem. 1993. 57, 1433-1438).

A solution of 8 (610 mg, 1.37 mmol) in methanolic ammonia (previously saturated at -10°C) (27 mL) was stirred at room temperature overnight. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (40 mL) and water (40 mL). The aqueous layer was washed with methylene chloride (2x 40 mL), concentrated under reduced pressure and coevaporated several times with absolute ethanol. Recrystallization from a mixture absolute ethanol/methanol gave 9 (215 mg, 61%) as a colorless and crystalline solid. Mp: 226-227 (dec.) (lit. 227 : Ref.6); UV (H₂O): χ_ax = 259 nm (ε = 10100), λ,™ = 228 nm (ε = 2200); HPLC 99.56%, -NMR (DMSO-d₆): δ 11.28 (s, IH, NH), 7.89 (d, IH, H-6, J_6-5 = 8.1 Hz), 5.80 (d, IH, H-l', J,._₂. = 7.1 Hz), 5.64 (d, IH, H-5, J_5-6 = 8.1 Hz), 5.24 (d, IH, OH-2', J_OH-2' = 6.5 Hz), 5.18 (t, IH, OH-5' JoH-5_' = JoH-5" = 5.2 Hz), 5.01 (d, IH, OH-3', J_0H-₃' = 5.0 Hz), 4.28 (dd, IH, H-2', J = 6.5 Hz, J = 12.2 Hz), 3.90 (t, IH, H-3', J₃..₂. = J₃._-0H' = 5.1 Hz), 3.30 (m, 2H, H-5' and H-5"), 1.06 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 517 (2M+H)⁺, 259 (M+H)⁺, 147 (S)⁺ FAB<0 m/z 515 (2M-H)^", 257 (M-H)^'. Example 10

Preparation of l-(5-0-Benzoyl-4-C-methyl-2, 3-0-acetyl~β-D-ribofuranosyl)4- thio-uracil (10)

Lawesson's reagent (926 mg, 2.29 mmol) was added under argon to a solution of 8 (1.46 g, 3.27 mmol) in anhydrous 1,2-dichloroethane (65 L) and the reaction mixture was stirred overnight under reflux. The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (1-2%) in chloroform] to give pure 10 (1.43 g, 95%>) as a yellow foam. Η-NMR (DMSO- dβ): δ 12.88 (s, IH, NH), 8.1-7.5 (m, 6H, C₆H₅CO and H-6), 6.27 (d, IH, H-l', J,._ ₂- = 7.51 Hz), 5.91 (br s, IH, H-5) 5.64 (m, 2H, H-2' and H-3'), 4.47 (d, IH, H-5', J₅'-₅" = 11.7 Hz), 4.36 (d, IH, H-5', ]₅>^' = 11.7 Hz), 2.11 (s, 3H, CH₃CO₂), 2.09 (s, 3H, CH₃CO₂), 1.39 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 925 (2M+H)⁺, 463 (M+H)⁺, 335 (S)⁺, 129 (BH₂)⁺, 105 (C₆H₅CO)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 461 (M-H)-, 127 (B)\ 121 (C₆H₅CO₂y, 59 (CH₃CO₂)^_.

Example 11

Preparation of l-(4-C-methyl-β-D-ribofuranosyl)4-thio-uracil (11)

A solution of 10 (500 mg, 1.08 mmol) in methanolic ammonia (previously saturated at -10°C) (27 mL) was stirred at room temperature overnight. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (40 ml) and water (40 mL). The aqueous layer was washed with methylene chloride (2x 40 mL), concentrated under reduced pressure. The crude material was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (5-7%) in methylene chloride] to give pure 11 (188 mg, 63%), which was lyophilized. Mp: 65-70 (dec); UV (methanol): λmax = 330 nm (ε = 20000) 246 nm (ε = 4200), λ_min = 275 nm (ε = 1500); ^!H- NMR (DMSO-de): δ 12.51 (bra, IH, NH), 7.81 (d, IH, H-6, J_6-5 = 7.6 Hz), 6.30 (d, IH, H-5, J_5-6 = 7.5 Hz), 5.77, (d, IH, H-l', J_r-2' = 6.7 Hz), 5.32 (d, IH, OH-2', JOH-2- = 6.1 Hz), 5.20 (t, IH, OH-5' J_0H-5_' = JOH-₅" = 5.2 Hz), 5.03 (d, IH, OH-3', JoH-3' = 5.2 Hz), 4.17 (dd, IH, H-2', J = 6.2 Hz, J = 12,0 Hz), 3.89 (t, IH, H-3', J₃.. ? = J₃'-_OH' = 5.1 Hz), 3.35 (m, 2H, H-5' and H-5"), 1.02 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 275 (M+H)⁺, 147 (S)⁺, 129(BH₂)⁺ FAB<0 m/z 547 (2M-H)^", 273 (M-H)^"' 127 (B)\

Example 12

Preparation of l-(4-C-methyl-β-D-ribofuranosyl)cytosine. hydrochloric form

(Ui

Compound 11 (890 mg, 1.93 mmol) was treated with methanolic ammonia (previously saturated at -10°C), (12 mL) at 100°C in a stainless-steel bomb for 3 hours, then cooled to room temperature. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (40 mL) and water (40 mL). The aqueous layer was washed with methylene chloride (2x 40 mL), concentrated under reduced pressure. The crude material was purified by silica gel column chromatography [eluent: methylene chloride/ methanol/ammonium hydroxide 65:30:5]. The collected fractions were evaporated under reduced pressure and in absolute ethanol (6.3 mL). To the solution was added a 2N hydrochloric acid solution (1.5 mL) and the mixture was stirred before being concentrated under reduced pressure. The procedure was repeated twice and 12 was precipitated from absolute ethanol. Mp: 213-214 (dec); UV (methanol): λ_max = 280 nm (ε = 9800), λ_min = 245 nm (ε = 3600); 1H- NMR (DMSO-dg): δ 9.82 (s, IH, NH₂), 8.72 (s, IH, NH₂), 8.34 (d, IH, H-6, J_6-5 = 7.8 Hz), 6.21 (d, IH, H-5, J_5-6 = 7.8 Hz), 5.83 (d, IH, H-l', J^. = 5.8 Hz), 4.22 (d, IH, OH-2', J_0H-2' = 6.5 Hz), 5.6-4.7 (m, 3H, OH-2', OH-3' and OH-5'), 4.28 (t, IH, H-2', J = 5.6 Hz), 3.99 (d, IH, H-3', J = 5.3 Hz), 3.43 (m, 2H, H-5' and H-5"), 1.14 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 515 (2M+H)⁺, 258 (M+H)⁺, 147 (S)⁺, 112 (BH₂)⁺ FAB<0 m/z 256 (M-H)-.

Example 13

Preparation of l-(5-0-Benzoyl-4-C-rnethyl-2,3-0-acetyl-β-D- ribofuranosyDthymine (13)

A suspension of thymine (384 mg, 3.04 mmol) was treated with hexamethyldisilazane (HMDS, 17 mL) and a catalytic amount of ammonium sulfate overnight under reflux. After cooling to room temperature, the mixture was evaporated under reduced pressure, and the residue, obtained as a colorless oil, was diluted with anhydrous 1,2-dichloroethane (6 mL). To the resulting solution was added 7 (1.0 g, 2.53 mmol) in anhydrous 1,2-dichloroethane (14 mL), followed by addition of trimethylsilyl trifluoromethanesulfonate (TMSTf, 0.98 L, 5.06 mmol). The solution was stirred for 5 hours at room temperature under argon atmosphere, then diluted with chloroform (150 mL), washed with the same volume of a saturated aqueous sodium hydrogen carbonate solution and finally with water (2x 100 mL). The organic phase was dried over sodium sulfate, then evaporated under reduced pressure. The resulting crude material was purified by silica gel column chromatography [eluent: 2% of methanol in chloroform] to afford pure 13 (1.09 g, 94%) as a foam. 1H-NMR (DMSO-d₆): δ 11.47 (s, IH, NH), 8.1-7.4 (m, 6H, C₆H₅CO and H-6), 5.98 (d, IH, H-l', J = 5.0 Hz), 5.5-5.7 (m, 2H, H-2' and H-3'), 4.42 (dd, 2H, H-5' and H-5", J = 11.6 Hz, J = 31.6 Hz), 2.12 (s, 3H, CH₃C0₂), 2.09 (s, 3H, CH₃CO₂), 1.60 (s, IH, CH₃), 1.37 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 461 (M+H)⁺, 335 (S)⁺, 105 (C₆H_sCO)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 459 (M-H)^", 125 (B)-, 121 (C₆H₅CO₂)-, 59 (CH₃CO₂)^'. Example 14

Preparation ofl-(4-C-methyl-β-D-ribofuranosyl)thymine (14)

The title compound can be prepared according to a published procedure from 13 (Waga, T.; Nishizaki, T.; Miyakawa, I.; Orhui, H.; Meguro, H. "Synthesis of 4'-C-methylnucleosides" Biosci. Biotechnol. Biochem. 1993, 57, 1433-1438).

A solution of 13 (1.09 g, 2.37 mmol) in methanolic ammonia (previously saturated at -10°C) (60 mL) was stirred at room temperature overnight. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (60 mL) and water (60 mL). The aqueous layer was washed with methylene chloride (2x 60 mL), concentrated under reduced pressure and coevaporated several times with absolute ethanol. Recrystallization from methanol gave 14 (450 mg, 70%) as a colorless and crystalline solid. Mp: 258-260 (dec.) (lit. 264 : Ref.6); UV (H₂O): λ_max = 264.4 nm (ε = 8800), ^ = 232.0 nm (ε = 2200); Η-NMR (DMSO-d₆): δ 11.29 (s, IH, NH), 7.75 (s, IH, H- 6), 5.82 (d, IH, H-l', J_V-τ = 7.2 Hz), 5.19 (m, 2H, OH-2', OH-5'), 5.02 (d, IH, OH-3', JoH-3' = 5.0 Hz), 4.21 (dd, IH, H-2', J = 6.4 Hz, J = 12.3 Hz), 3.92 (t, IH, H-3', J₃._-2. = J₃.-_OH' = 5.0 Hz), 3.30 (m, 2H, H-5' and H-5"), 1.78 (s, 3H, CH₃), 1.09 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 545 (2M+H)⁺, 365 (M+G+H)⁺, 273 (M+H)⁺, 147 (S)⁺, 127 (B+2H)⁺, FAB<0 m/z 543 (2M-H)^", 271 (M-H)-, 125 (B)^_; [α]_D ²⁰ - 32.0 (c = 0.5 in H₂O, litt. -26.4).

Example 15

Preparation ofl-(5,2,3-Tri-0-acetyl-4-C-methyl-β-D-ribofuranosyl)thvmine (15)

A solution of 14 (200 mg, 0.735 mmol) in anhydrous pyridine (7.4 ml) was treated with acetic anhydride (1.2 mL) and stirred at room temperature for 3 hours. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (0-5%) in .methylene chloride] to afford pure 15 (0.400 g, quantitative yield) as a foam. 1H-NMR (DMSO-d₆₎: δ 11.45 (s, IH, NH), 7.56 (s, IH, H-6), 5.90 (d, IH, H-l', J_r-2. = 4.8 Hz), 5.5-5.4 ( , 2H, H-2' and H-3'), 4.3-4.0 (m, 2H, H-5' and H-5"), 2.1-2.0 (m, 9H, 3 CH₃CO₂), 1.78 (s, IH, CH₃), 1.20 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 797 (2M+H)⁺, 399 (M+H)⁺, 339 (M-CH₃CO₂)⁺, 273 (S)⁺, 127 (BH₂)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 795 (2M-H)-, 397 (M-H)-, 355 (M-CH₃CO)^", 125 (B)^", 59 (CH₃CO₂)^".

Example 16

Preparation of l-(5.2.3-Tri-0-acetyl-4-C-methyl~β-D-ribofuranosyl)-4-thio- thvmine (16)

Lawesson's reagent (119 mg, 0.29 mmol) was added under argon to a solution of 15 (0.167 g, 4.19 mmol) in anhydrous 1,2-dichloroethane (11 mL) and the reaction mixture was stirred overnight under reflux. The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (1-2%) in chloroform] to give pure 16 (0.165 g, 95%) as a yellow foam. H-NMR (DMSO- d₆): δ 12.81 (s, IH, NH), 7.64 (s, IH, H-6), 5.84(d, IH, H-l', J_r-2. = 4.66 Hz), 5.5-5.4 (m, 2H, H-2' and H-3'), 4.11 (dd, 2H, H-5' and H-5", J = 11.7 Hz, J = 31.3 Hz), 2.0-1.8 ( , 12H, 3 CH₃CO₂ and CH₃), 1.33 (s, 3H, CH ); MS (matrix GT): FAB>0 m/z 829 (2M+H)⁺, 415 (M+H)⁺ ₅ 273 (S)⁺, 143 (BH₂)⁺, 43 (CH₃CO)⁺ FAB<0 m/z 827 (2M-H)^", 413 (M-H)-' 141 (B)^", 59 (CH₃CO₂)^".

In a similar manner, the following nucleosides of Formula II are prepared, using the appropriate sugar and pyrimidine bases.

(II) wherein:

Example 17

Preparation of l-(4-C-methyl-β-D-ribofurarιosyl)-5-methyl-cytosine (17), hydrochloride form

Compound 16 (0.160 g, 0.386 mmol) was treated with methanolic ammonia (previously saturated at -10°C), (10 mL) at 100°C in a stainless-steel bomb for 3 hours, then cooled to room temperature. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (30 mL) and water (30 mL). The aqueous layer was washed with methylene chloride (2x 30 mL), concentrated under reduced pressure. The crude material was purified by silica gel column chromatography [eluent: 20% methanol in methylene chloride] to afford l-(4-C-methyl-β-D-ribofuranosyl)-5- methyl-cytosine (60 mg, 57%). This compound was dissolved in EtOH 100 (1.5 mL), treated with a 2N hydrochloric acid solution (0.3 L), and the mixture was stirred before being concentrated under reduced pressure. The procedure was repeated twice and 17 was precipitated from absolute ethanol. Mp: 194-200 (dec); UV (H₂O): A™* = 275.6 nm (ε = 7300), λ^ = 255 nm (ε = 4700); HPLC 100%, Η-NMR (DMSO-de): δ 9.34 and 9.10 (2s, 2H, NH₂), 8.21 (s, IH, H-6), 5.80 (d, IH, H-l', J_r-ϊ = 6.0 Hz), 5.3-4.3 (m, 3H, OH-2', OH-3' and OH-5'), 4.21 (t, IH, H-2', J= 5.7 Hz), 3.98 (d, IH, H-3'₅ J = 5.3 Hz), 3.5-3.3 (m, 2H, H-5' and H-5"), 1.97 (s, 3H, CH ), 1.12 (s, 3H, CH₃).

Example 18

Preparation of O-6-Diphenylcarbamoyl-N -isobutyryl-9-(2,3-di-0-acetyl-5-0- benzoyl-4-C-methyl-β-D-ribofuranosyl)suanine (18)

To a suspension of O-6-diphenylcarbamoyl-N²-isobutyrylguanine (1.80 g, 4.33 mmol) in anhydrous toluene (20 mL) was added N,O- bis(trimethylsilyl)acetamide (1.92 mL, 7.9 mmol). The reaction mixture was allowed to warm under reflux for 1 hour. Compound 7 (1.55 g, 3.93 mmol) was dissolved in toluene (10 mL) and trimethylsilyltrifluoromethanesulfonate (TMSTf) (915 mL, 4.72 mmol) was added. The mixture was heated under reflux for 30 minutes. The solution was then cooled to room temperature and neutralized with a 5% aqueous sodium hydrogen carbonate solution. The reaction mixture was diluted with ethyl acetate (200 mL). The organic phase was washed with a 5% aqueous sodium hydrogen carbonate solution (150 mL) and with water (2x 150 mL). The organic layer was dried over Na₂SO and evaporated to dryness. The residue was purified by silica gel column chromatography [eluent: stepwise gradient of diethyl ether (70-90%) in petroleum ether] to afford pure 18 (1.62 g, 55%) as a foam.

Example 19

Preparation of9-(4-C-methyl-β-D-ribofuranosyl) suanine (19)

The title compound can be prepared according to a published procedure from 18 (Waga, T.; Nishizaki, T.; Miyakawa, I.; Orhui, H.; Meguro, H. "Synthesis of 4'-C-methylnucleosides" Biosci. Biotechnol. Biochem. 1993, 57, 1433-1438).

A solution of 18 (1.50 g, mmol) in methanolic ammonia (previously saturated at -10°C) (20 mL) was stirred at room temperature overnight. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (60 mL) and water (60 mL). The aqueous layer was washed with methylene chloride (2x 60 L), concentrated under reduced pressure. The residue was purified by an RP 18 column chromatography [eluent water/acetonitrile 95/5] to afford pure 19 (380 mg, 60%). Recrystallization from water gave 19 as a crystalline solid. Mp > 300 (dec), UV (H₂O): λ_πiax = 252 nm (ε = 14500), 1H-NMR (DMSO-d₆): δ 10.64 (s, IH, NH), 7.95 (s, IH, H-8), 6.45 (si, 2H, NH₂), 5.68 (d, IH, H-l', J_{l y} = 7.45 Hz), 5.31 (d, IH, OH, OH-2',J_OH-2_' = 6.8 Hz), 5.17 (t, IH, OH, OH-5', J = 5.5 Hz), 5.07 (d, IH, OH-3', J_OH-3' = 4.5 Hz), 4.65 (dd, IH, H-2', J = 7.1 Hz, J = 12.2 Hz), 4.00 (t, IH, H-3', J₃._₂. = J_3'-OH' = 4.8 Hz), 3.41 (m, 2H, H-5' and H-5"), 1.12 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 595 (2M+H)⁺, 390 (M+G+H)⁺, 298 (M+H)⁺, 152 (B+2H)⁺, FAB<0 m/z 593 (2M-H)\ 296 (M-H)-, 150 (B)^".

Example 20

9-(2,3-di-0-acetyl-5-0-benzoyl-4-C-methyl-β-D-ribofurarιosyl)adenine (20)

A solution of 7 (1.10 g, 2.79 mmol) in anhydrous acetonitrile (50 ml) was treated with adenine (452.4 mg, 3.35 mmol) and stannic chloride (SnCl , 660 μL, 5.58 mmol) and stirred at room temperature overnight. The solution was concentrated under reduced pressure, diluted with chloroform (100 L) and treated with a cold saturated aqueous solution of NaHCO₃ (100 ml). The mixture was filtered on celite, and the precipitate was washed with hot chloroform. The filtrates were combined, washed with water (100 ml) and brine (100 ml), dried (Na₂SO₄), and evaporated under reduced pressure. The residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (3-5%) in dichloromethane] to afford pure 20 (977 mg, 77%) as a white foam. Η-NMR (DMSO-de): δ 8.31-7.49 (m, 7H, C₆H₅CO, H-2 and H-8), 7.37 (Is, 2H, NH₂) 6.27 (m, 2H, H-l' and H-3'), 5.90 ( , IH, H-2'), 4.60 (d, IH, H-5', J = 11.7 Hz), 4.35 (d, IH, H-5"), 2.17 (s, 3H, CH₃CO₂), 2.06 (s, 3H, CH₃CO₂), 1.42 (s, 3H, CH₃). Example 21

Preparation of9-(4τC-methyl-β-D-ήbofuranosyl) adenine (21)

The title compound can be prepared according to a published procedure from 20 (Waga, T.; Nishizaki, T.; Miyakawa, I.; Orhui, H.; Meguro, H. "Synthesis of 4'-C-methyhτucleosides" Biosci. Biotechnol. Biochem. 1993, 57, 1433-1438).

A solution of 20 (970 mg, 2.08 mmol) in methanolic ammonia (previously saturated at -10°C) (50 mL) was stirred at room temperature overnight. The solvent was evaporated under reduced pressure and the residue was partitioned between methylene chloride (100 ml) and water (100 ml). The aqueous layer was washed with methylene chloride (2x 100 mL), and concentrated under reduced pressure. The residue was purified by silica gel column chromatography [eluent: stepwise gradient of methanol (10-30%) in ethyl acetate] to afford pure 21 (554 mg, 95%). Crystallization from methanol/ethyl acetate gave 21 as a white solid. Mp: 96-97 (dec); -NMR (DMSO-d₆): δ 8.33 (s, IH, H-2), 8.13 (s, IH, H-8), 7.36 (brs, 2H, NH2), 5.84 (d, IH, H-l', J_r-2. = 7.4 Hz), 5.69 (dd, IH, OH-5', J = 4.2 Hz and J = 7.8 Hz), 5.33 (d, IH, OH-2', J = 6.6 Hz), 5.13 (d, IH, OH-3', J = 4.4 Hz), 4.86 (m, IH, H-2'), 4.04 (t, IH, H-3'), 3.58-3.32 (m, 2H, H-5' and H-5"), 1.15 (s, 3H, CH₃); MS (matrix GT): FAB>0 m/z 563 (2M+H)⁺, 374 (M+G+H)⁺, 282 (M+H)⁺, 136 (B+2H)⁺, FAB<0 m/z 561 (2M-H)^", 280 (M-H)^", 134 (B)^".

In a similar manner, the following nucleosides of Formula I are prepared, using the appropriate sugar and purine bases.

(I) wherein:

Alternatively, the following nucleosides of Formula III are prepared, using the appropriate sugar and pyrimidine or purine bases.

(III) wherein:

Alternatively, the following nucleosides of Formula TV are prepared, using the appropriate sugar and pyrimidine or purine bases.

(IV) wherein

Alternatively, the following nucleosides of Formula V are prepared, using the appropriate sugar and pyrimidine or purine bases.

(V) wherein:

Alternatively, the following nucleosides of Formula VI are prepared, using the appropriate sugar and pyrimidine or purine bases.

(VI) wherein: VII. Anti-Flavivirus or Pestivirus Activity

Compounds can exhibit anti-flavivirus or pestivirus activity by inhibiting flavivirus or pestivirus polymerase, by inhibiting other enzymes needed in the replication cycle, or by other pathways.

EXAMPLES

The test compounds were dissolved in DMSO at an initial concentration of 200 μM and then were serially diluted in culture medium.

Unless otherwise stated, baby hamster kidney (BHK-21) (ATCC CCL-10) and Bos Taurus (BT) (ATCC CRL 1390) cells were grown at 37°C in a humidified CO₂ (5%) atmosphere. BHK-21 cells were passaged in Eagle MEM additioned of 2 mM L-glutamine, 10% fetal bovine serum (FBS, Gibco) and Earle's BSS adjusted to contain 1.5 g/L sodium bicarbonate and 0.1 mM non- essential amino acids. BT cells were passaged in Dulbecco's modified Eagle's medium with 4 M L-glutamine and 10% horse serum (HS, Gibco), adjusted to contain 1.5 g/L sodium bicarbonate, 4.5 g/L glucose and 1.0 mM sodium pyruvate. The vaccine strain 17D (YFV-17D) (Stamaril®, Pasteur Merieux) and Bovine Viral Diarrhea virus (BVDV) (ATCC VR-534) were used to infect BHK and BT cells, respectively, in 75 cm² bottles. After a 3 day incubation period at 37°C, extensive cytopathic effect was observed. Cultures were freeze-thawed three times, cell debris were removed by centrifugation and the supernatant was aliquoted and stored at -70°C. YFV-17D and BVDV were titrated in BHK-21 and BT cells, respectively, that were grown to confiuency in 24-well plates.

Ill Example 22

Phosphorylation Assay of Nucleoside to Active Triphosphate

To determine the cellular metabolism of the compounds, HepG2 cells are obtained from the American Type Culture Collection (Rockville, MD), and are grown in 225 cm² tissue culture flasks in minimal essential medium supplemented with non-essential amino acids, 1% penicillin-streptomycin. The medium is renewed every three days, and the cells are subcultured once a week. After detachment of the adherent monolayer with a 10 minute exposure to 30 mL of trypsin-EDTA and three consecutive washes with medium, confluent HepG2 cells are seeded at a density of 2.5 x 10⁶ cells per well in a 6-well plate and exposed to 10 μM of [³H] labeled active compound (500 dpm/pmol) for the specified time periods. The cells are maintained at 37°C under a 5% CO₂ atmosphere. At the selected time points, the cells are washed three times with ice-cold phosphate-buffered saline (PBS). Intracellular active compound and its respective metabolites are extracted by incubating the cell pellet overnight at - 20°C with 60% methanol followed by extraction with an additional 20 μL of cold methanol for one hour in an ice bath. The extracts are then combined, dried under gentle filtered air flow and stored at-20°C until HPLC analysis.

Example 23

Bioavailability Assay in Cvnomolgus Monkeys

Within 1 week prior to the study initiation, the cynomolgus monkey is surgically implanted with a chronic venous catheter and subcutaneous venous access port (VAP) to facilitate blood collection and underwent a physical examination including hematology and serum chemistry evaluations and the body weight was recorded. Each monkey (six total) receives approximately 250 μCi of H activity with each dose of active compound at a dose level of 10 mg/kg at a dose concentration of 5 mg/mL, either via an intravenous bolus (3 monkeys, IV), or via oral gavage (3 monkeys, PO). Each dosing syringe is weighed before dosing to gravimetrically determine the quantity of formulation administered. Urine samples are collected via pan catch at the designated intervals (approximately 18-0 hours pre-dose, 0-4, 4-8 and 8-12 hours post-dosage) and processed. Blood samples are collected as well (pre-dose, 0.25, 0.5, 1, 2, 3, 6, 8, 12 and 24 hours post-dosage) via the chronic venous catheter and VAP or from a peripheral vessel if the chronic venous catheter procedure should not be possible. The blood and urine samples are analyzed for the maximum concentration (C_ma ), time when the maximum concentration is achieved (T_max), area under the curve (AUC), half life of the dosage concentration (T_/J, clearance (CL), steady state volume and distribution (V_ss) and bioavailability (F).

Example 24

Bone Marrow Toxicity Assay

Human bone marrow cells are collected from normal healthy volunteers and the mononuclear population are separated by Ficoll-Hypaque gradient centrifugation as described previously by Sommadossi J-P, Carlisle R. "Toxicity of 3'-azido-3'-deoxythymidine and 9-(l,3-dihydroxy-2-propoxymethyl)guanine for normal human hematopoietic progenitor cells in vitro" Antimicrobial Agents and Chemotherapy 1987; 31:452-454; and Sommadossi J-P, Schinazi RF, Chu CK, Xie M-Y. "Comparison of cytotoxicity of the (-)- and (+)-enantiomer of 2',3'-dideoxy-3'-thiacytidine in normal human bone marrow progenitor cells" Biochemical Pharmacology 1992; 44:1921-1925. The culture assays for CFU- GM and BFU-E are performed using a bilayer soft agar or methylcellulose method. Drugs are diluted in tissue culture medium and filtered. After 14 to 18 days at 37°C in a humidified atmosphere of 5% CO₂ in air, colonies of greater than 50 cells are counted using an inverted microscope. The results are presented as the percent inhibition of colony formation in the presence of drug compared to solvent control cultures.

Example 25

Mitochondria Toxicity Assay

HepG2 cells are cultured in 12-well plates as described above and exposed to various concentrations of drugs as taught by Pan-Zhou X-R, Cui L, Zhou X-J, Sommadossi J-P, Darley-Usmer VM. "Differential effects of antiretroviral nucleoside analogs on mitochondrial function in HepG2 cells" Antimicrob Agents Chemother 2000; 44:496-503. Lactic acid levels in the culture medium after 4 day drug exposure are measured using a Boehringer lactic acid assay kit. Lactic acid levels are normalized by cell number as measured by hemocytometer count.

Example 26

Cytotoxicity Assay

Cells are seeded at a rate of between 5 x 10³ and 5 x 10⁴/well into 96-well plates in growth medium overnight at 37°C in a humidified CO₂ (5%) atmosphere. New growth medium containing serial dilutions of the drugs is then added. After incubation for 4 days, cultures are fixed in 50% TCA and stained with sulforhodamineB. The optical density was read at 550 nm. The cytotoxic concentration was expressed as the concentration required to reduce the cell number by 50% (CC₅₀). The preliminary results are tabulated in the Table 1 below. Table 1: MDBK versus Human Hepatoma

CCso, μM

Compound MDBK β-D-4'-CH₃-riboG >250 β-D-4'-CH₃-ribo-4- >250 thioU β-D-4'-CH₃-riboC >250 β-D-4'-CH₃-ribo-5- >167 fluoroU β-D-4'-CH₃-riboT >250 β-D-4'-CH₃-riboA >250

Example 27

Cell Protection Assay (CPA)

The assay is performed essentially as described by Baginski, S. G.; Pevear, D. C; Seipel, M.; Sun, S. C. ; Benetatos, C. A.; Chunduru, S. K.; Rice, C. M. and M. S. CoUett "Mechanism of action of a pestivirus antiviral compound" PNAS USA 2000, 97(14), 7981-7986. MDBK cells (ATCC) are seeded onto 96-well culture plates (4,000 cells per well) 24 hours before use. After infection with BVDV (strain NADL, ATCC) at a multiplicity of infection (MOI) of 0.02 plaque forming units (PFU) per cell, serial dilutions of test compounds are added to both infected and uninfected cells in a final concentration of 0.5%> DMSO in growth medium. Each dilution is tested in quadruplicate. Cell densities and virus inocula are adjusted to ensure continuous cell growth throughout the experiment and to achieve more than 90% virus- induced cell destruction in the untreated controls after four days post-infection. After four days, plates are fixed with 50% TCA and stained with sulforhodamine B. The optical density of the wells is read in a microplate reader at 550 nm. The 50% effective concentration (EC₅0) values are defined as the compound concentration that achieved 50% reduction of cytopathic effect of the virus. The results are tabulated in Table 2.

Table 2: Cell Protection Assay

Compound ECso, μM CCso, μM β-D-4'-CH₃-riboG 43 >250 β-D-4'-CH₃-ribo-4-thioU >250 >250 β-D-4'-CH₃-riboC 9 >250 β-D-4'-CH₃-ribo-5-fluoroU >167 >167 β-D-4'-CH₃-riboT >250 >250 β-D-4'-CH₃-riboA >250 >250

Example 28

Plaque Reduction Assay

For each compound the effective concentration is determined in duplicate 24-well plates by plaque reduction assays. Cell monolayers are infected with 100 PFU/well of virus. Then, serial dilutions of test compounds in MEM supplemented with 2% inactivated serum and 0.75% of methyl cellulose are added to the monolayers. Cultures are further incubated at 37°C for 3 days, then fixed with 50% .ethanol and 0.8% Crystal Violet, washed and air-dried. Then plaques are counted to determine the concentration to obtain 90% virus suppression.

Example 29

Yield Reduction Assay

For each compound the concentration to obtain a 6-log reduction in viral load is determined in duplicate 24-well plates by yield reduction assays. The assay is performed as described by Baginski, S. G.; Pevear, D. C; Seipel, M.; Sun, S. C. C; Benetatos, C. A.; Chunduru, S. K.; Rice, C. M. and M. S. CoUett "Mechanism of action of a pestivirus antiviral compound" PNAS USA 2000, 97(14), 7981-7986, with minor modifications. Briefly, MDBK cells are seeded onto 24-well plates (2 x 105 cells per well) 24 hours before infection with BVDV (NADL strain) at a multiplicity of infection (MOI) of 0.1 PFU per cell. Serial dilutions of test compounds are added to cells in a final concentration of 0.5% DMSO in growth medium. Each dilution is tested in triplicate. After three days, cell cultures (cell monolayers and supernatants) are lysed by three freeze-thaw cycles, and virus yield is quantified by plaque assay. Briefly, MDBK cells are seeded onto 6-well plates (5 x 105 cells per well) 24 h before use. Cells are inoculated with 0.2 mL of test lysates for 1 hour, washed and overlaid with 0.5% agarose in growth medium. After 3 days, cell monolayers are fixed with 3.5% formaldehyde and stained with 1% crystal violet (w/v in 50% ethanol) to visualize plaques. The plaques are counted to determine the concentration to obtain a 6-log reduction in viral load.

This invention has been described with reference to its preferred embodiments. Variations and modifications of the invention, will be obvious to those skilled in the art from the foregoing detailed description of the invention.

Claims

We Claim:

1. A method for the treatment or prophylaxis of a flaviviruses and pestiviruses infectioh in a host, comprising administering an anti-virally effective amount of a compound of Formula I:

(I) or a pharmaceutically acceptable salt or prodrug thereof, wherein: R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate; a stabilized phosphate prodrug; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate; Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴;

1 ?

X and X are independently selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR^S or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

2. A method for the treatment or prophylaxis of a flaviviruses and pestiviruses infection in a host, comprising administering an anti-virally effective amount of a compound of Formula II:

(II) or a pharmaceutically acceptable salt or prodmg thereof, wherein: R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate, a stabilized phosphate prodmg; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherem R 1 , R 9 and R ^"^ are independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X¹ is selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR^NR⁵ or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

3. A method for the treatment or prophylaxis of a flaviviruses and pestiviruses infection in a host, comprising administering an anti-virally effective amount of a compound selected from Formulas III, IV and V, or a pharmaceutically acceptable salt or prodmg thereof, is provided:

wherein: Base is a purine or pyrimidine base;

R¹, R² and R³ are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodmg; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(0)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), CF_3j chloro, bromo, fluoro, iodo, NO₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

4. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an anti-virally effective amount of a compound of Formula VI, or a pharmaceutically acceptable salt or prodmg thereof:

(VI) wherein:

Base is a purine or pyrimidine base;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), CF₃₎ chloro, bromo, fluoro, iodo, NO₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

5. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

or a pharmaceutically acceptable salt or prodmg thereof.

6. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture :

or a pharmaceutically acceptable salt or prodmg thereof.

7. A ^■ method for the treatment or prophylaxis of a flaviviruses and pestiviruses infection in a host, comprising administering an antivirally effective amount of a compound of the structure:

or a pharmaceutically acceptable salt or prodmg thereof.

8. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

or a pharmaceutically acceptable salt or prodmg thereof.

9. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

or a pharmaceutically acceptable salt or prodmg thereof.

10. A method for the treatment or prophylaxis of a flavivimses and pestivirases infection in a host, comprising administering an antivirally effective amount of a compound of the structure:

or a pharmaceutically acceptable salt or prodrug thereof.

11. A method for the treatment or prophylaxis of a flaviviruses and pestiviruses infection in a host, comprising administering an anti-virally effective amount of a compound of Formula I:

(I) or a pharmaceutically acceptable salt or prodrag thereof, in combination or alternation with one or more other antivirally effective agents, wherein: R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate; a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate; Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴;

X 1 and X 9 are independently selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

12. A method for the treatment or prophylaxis of a flavivimses and pestivirases infection in a host, comprising administering an anti-virally effective amount of a compound of Formula II:

(II) or a pharmaceutically acceptable salt or prodmg thereof, in combination or alternation with one or more other antivirally effective agents, wherein: R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate, a stabilized phosphate prodmg; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X is selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁴; and R and R⁵ are independently hydrogen, acyl, or alkyl.

13. A method for the treatment or prophylaxis of a flavivimses and pestivirases infection in a host, comprising administering an anti-virally effective amount of a compound selected from Formulas III, IV and V:

(III) (IV) (V) or a pharmaceutically acceptable salt or prodrug thereof, in combination or alternation with one or more other antivirally effective agents, wherein:

Base is a purine or pyrimidine base;

R , R² and R³ are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R^!, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), CF_3j chloro, bromo, fluoro, iodo, NO₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

14. A method for the treatment or prophylaxis of a flaviviruses and pestiviruses infection in a host, comprising administering an anti-virally effective amount of a compound of Formula VI, or a pharmaceutically acceptable salt or prodrag thereof:

(VI) or a pharmaceutically acceptable salt or prodrag thereof, in combination or alternation with one or more other antivirally effective agents, wherein:

Base is a purine or pyrimidine base; 1 9 ^

R , R and R are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), CF_3; chloro, bromo, fluoro, iodo, N0₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂;

X is O, S, SO₂ or CH₂.

R⁷ and R⁹ are independently hydrogen, OR², hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br-vinyl, -C(O)0(alkyl), -C(0)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), chlorine, bromine, iodine, NO₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, - N(acyl)₂;

R⁸ and R¹⁰ are independently H, alkyl, chlorine, bromine or iodine; alternatively, R⁷ and R⁹, R⁷ and R¹⁰, R⁸ and R⁹, or R⁸ and R¹⁰ can come together to form a pi bond; and

X is O, S, SO₂ or CH₂.

15. A method for the treatment or prophylaxis of a flavivimses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture: or a pharmaceutically acceptable salt or prodmg thereof, in combination or alternation with one or more antivirally effective agents.

16. A method for the treatment or prophylaxis of a flaviviruses and pestivirases infection in a host, comprising administering an antivirally effective amount of a compound of the structure:

or a pharmaceutically acceptable salt or prodmg thereof, in combination or alternation with one or more antivirally effective agents.

17. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

18. A method for the treatment or prophylaxis of a flavivimses and pestivirases infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

or a pharmaceutically acceptable salt or prodrag thereof, in combination or alternation with one or more antivirally effective agents.

19. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture:

20. A method for the treatment or prophylaxis of a flaviviruses and pestivimses infection in a host, comprising administering an antivirally effective amount of a compound of the stracture: or a pharmaceutically acceptable salt or prodmg thereof, in combination or alternation with one or more antivirally effective agents.

21. Method of treatment as described in any of the preceding claims 1-21, wherein the said compound is in the form of a dosage unit.

22. Method of treatment as described in claim 21, wherein the dosage unit contains 10 to 1500 mg of said compound.

23. Method of treatment as described in claim 21 or 22, wherein said dosage unit is a tablet or capsule.

24. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of

(i) (ϋ) (iii)

(iv) (v) (vi)

wherein A, G, and L are each independently CH or N;

D is N, CH, C-CN, C-NO₂, C-Q_-3 alkyl, C-NHCONH₂, C- CSNQ^πQ", CCOOQ¹¹, C-C(=NH)NH₂, C-hydroxy, C-Cι_-3alkoxy,C-amino, C-C_M alkylamino, C-di(C_M alkyl)amino, C-halogen, C-(l,3-oxazol-2-yl), C-(l,3- thiazol-2-yl), or C-(imidazol-2-yl); wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and Cι_-3 alkoxy; E is N or CQ⁵; W is O, S, orNR;

R is H, OH, alkyl;

Q⁶ is H, OH, SH, NH₂, C_M alkylamino, di(C_1-4 alkyl)amino, C_3-6 cycloalkylamino, halogen,

C_M alkyl, C_M alkoxy, or CF₃;

Q⁵ is H, Ci-e alkyl, C_2-6 alkenyl, C_2-6 alkynyl, C_]-4 alkylamino, CF₃, halogen, N, CN, NO₂, NHCONH₂, CONQ^πQ^π, CSNQ^πQ^π, COOQ¹¹, C(=NH)NH₂, hydroxy, Cι- alkoxy,amino, C_M alkylamino, di(C_1- alkyl)amino, halogen, l,3-oxazol-2-yl, l,3-thiazol-2-yl, or imidazol-2-yl; wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and _-3 alkoxy;

Q⁷ and Q¹⁴ are each independently selected from the group consisting of H, CF₃, OH, SH, OR, SR C_M alkyl, amino, C_M alkylamino, C_3-6 cycloalkylamino, and di(C alkyl)amino;

Q¹¹ is independently H or C ι ^ alkyl;

Q is H, halogen, CN, carboxy, C_M alkyloxycarbonyl, N₃, amino, C alkylamino, di(C alkyl)amino, hydroxy, Ci-g alkoxy, Cι_-6 alkylthio, Cι_-6 alkylsulfonyl,'(C_M alkyl)0-2 aminomethyl, N, CN, NO₂, C,_-3 alkyl, NHCONH₂,

CONQ^πQⁿ, CSNQV, COOQⁿ, C(=NH)NH₂, l,3-oxazol-2-yl, l,3-thiazol-2- yl, or imidazol-2-yl, wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and

Cι-₃ alkoxy.

25. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of:

CD) (E)

wherein:

Ti and T₂ are independently selected from N, CH, or C-Q¹⁶;

Q vl6 , U, and Y are independently selected from O, H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl, -O-alkyl, -O-alkenyl, -O- alkynyl, -O-aryl, -O-aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N-aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S- cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH₂, CO₂-alkyl, CONH-alkyl, CON- dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_raNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mNO₂, (CH₂)_mCONH₂, C alkylamino, di(C alkyl)amino, C_3-6 cycloalkylamino, C_M alkoxy, C_1-4 alkoxycarbonyl, Cι_-6 alkylthio, Cι.₆ alkylsulfonyl, (C_M alkyl)_0-2 aminomethyl, or-NHC(=NH)NH₂;

R⁴ and R⁵ are independently selected from hydrogen, acyl, or alkyl; m is 0-10;

Z is S, SO, SO2, C=O, or NQ²⁰;

Q²⁰ is H or alkyl; and

V] and V₂ are independently selected from CH or N;

26. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of:

(F) (G) (H) (I) wherein: T₃ and T are independently selected from N or CQ²²;

Q is independently selected from O, H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl,-O-alkyl, -O-alkenyl, -O-alkynyl, -O-aryl, -O- aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N- aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S-cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH₂, COz-alkyl, CONH-alkyl, CON-dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_mNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mN0₂, (CH₂)_mCONH₂, C alkylamino, di(CM alkyl)amino, C_3-6 cycloalkylamino, C_M alkoxy, C alkoxycarbonyl, Cue alkylthio, Cι-₆ alkylsulfonyl, (C1-4 alkyl)o_-2 aminomethyl, or -NHC(=NH)NH₂;

T₆, T₇, T₈, T₉, Tio, T_H, and T₎₂ are independently selected from N or CH;

U₂ is H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR R⁵ or SR⁵;

Y₂ is O, S, NH, NR or CQ²⁴Q²⁶ where R is H, OH, or alkyl;

Q²⁴ and Q²⁶ are independently selected from H, alkyl, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵.

27. Use of the compound of Formula I, its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C vims infection in a host:

(I) wherein:

R , R and R are independently H, mono-phosphate, di-phosphate, triphosphate; a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X¹ and X² are independently selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR^R⁵ or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

28. Use of the compound of Formula II, its pharmaceutically acceptable salts or prodmgs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C vims infection in a host:

(II) wherein:

R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X¹ is selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

29. Use of the compound of Formula III, IV and V, its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C virus infection in a host:

(III) (IV) (V) wherein:

Base is a purine or pyrimidine base;

R¹, R² and R³ are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodrug; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate; R is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), CF_3> chloro, bromo, fluoro, iodo, N0₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

30. Use of the compound of Formula VI or its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C virus infection in a host:

(VI) wherein:

Base is a purine or pyrimidine base;

R¹, R² and R³ are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -O(lower alkyl), -O(alkenyl), CF_3ι chloro, bromo, fluoro, iodo, N0₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and X is O, S, SO₂ or CH₂.

31. Use of the compound of stracture:

or its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C virus infection in a host.

32. Use of the compound of stracture:

or its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis

C viras infection in a host.

33. Use of the compound of structure: or its pharmaceutically acceptable salts or prodrags thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C vims infection in a host.

34. Use of the compound of stracture:

or its pharmaceutically acceptable salts or prodrags thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C virus infection in a host.

35. Use of the compound of stracture:

or its pharmaceutically acceptable salts or prodrugs thereof in the manufacture of, a medicament for the treatment and prophylaxis of a hepatitis C virus infection in a host.

36. Use of the compound of structure:

or its pharmaceutically acceptable salts or prodmgs thereof in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C viras infection in a host.

37. Use of compound of Formula I:

(I) or its pharmaceutically acceptable salts or prodrags thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C viras infection in a host, wherein: R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate; a stabilized phosphate prodmg; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R and R³ are independently H or phosphate;

Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X¹ and X² are independently selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁴; and R⁴ and R⁵ are independently hydrogen, acyl, or alkyl.

38. Use of compound of Formula II:

(II) or its pharmaceutically acceptable salts or prodmgs thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C vims infection in a host, wherein:

R¹, R² and R³ are independently H, mono-phosphate, di-phosphate, triphosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² and R³ are independently H or phosphate; Y is hydrogen, bromo, chloro, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁴; X¹ is selected from the group consisting of H, alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴NR⁵ or SR⁴; and R and R⁵ are independently hydrogen, acyl, or alkyl.

39. Use of compound of Formulas III, IV and V:

(III) (IV) (V) or its pharmaceutically acceptable salts or prodrags thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C viras infection in a host, wherein:

Base is a purine or pyrimidine base;

R 1 , R9 and R "^ are independently H; mono-phosphate, di-phosphate, tn-phosphate, a stabilized phosphate prodrag; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), CF_3> chloro, bromo, fluoro, iodo, N0₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂; and

X is O, S, SO₂ or CH₂.

40. Use of compound of Formulas VI:

(VI) or its pharmaceutically acceptable salts or prodmgs thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C viras infection in a host, wherein:

Base is a purine or pyrimidine base;

R¹, R² and R³ are independently H; mono-phosphate, di-phosphate, tri-phosphate, a stabilized phosphate prodmg; acyl; alkyl; sulfonate ester; a lipid, a phospholipid; an amino acid; a carbohydrate; a peptide; a cholesterol; or other pharmaceutically acceptable leaving group which when admimstered in vivo is capable of providing a compound wherein R¹, R² or R³ is independently H or phosphate;

R⁶ is hydroxy, alkyl, azido, cyano, alkenyl, alkynyl, Br-vinyl, 2-Br-ethyl, - C(O)O(alkyl), -C(O)O(lower alkyl), -O(acyl), -0(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), CF_3j chloro, bromo, fluoro, iodo, N0₂, NH₂, - NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, -N(acyl)₂;

X is O, S, SO₂ or CH₂.

R⁷ and R are independently hydrogen, OR², hydroxy, alkyl (including lower alkyl), azido, cyano, alkenyl, alkynyl, Br-vinyl, -C(0)0(alkyl), -C(0)0(lower alkyl), -O(acyl), -O(lower acyl), -O(alkyl), -0(lower alkyl), -O(alkenyl), chlorine, bromine, iodine, N0₂, NH₂, -NH(lower alkyl), -NH(acyl), -N(lower alkyl)₂, - N(acyl)₂; R and R .10 a . re independently H, alkyl, chlorine, bromine or iodine; alternatively, R⁷ and R⁹, R⁷ and R¹⁰, R⁸ and R⁹, or R⁸ and R¹⁰ can come together to form a pi bond; and

X is O, S, S0₂ or CH₂.

41. Use of compound of stracture :

or its pharmaceutically acceptable salts or prodrags thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the freatment and prophylaxis of a hepatitis

C virus infection in a host.

42. Use of compound of structure:

or its pharmaceutically acceptable salts or prodrugs thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis C vims infection in a host.

43. Use of compound of structure:

or its pharmaceutically acceptable salts or prodrags thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis

C viras infection in a host.

44. Use of compound of stracture:

or its pharmaceutically acceptable salts or prodrugs thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis

C viras infection in a host.

45. Use of compound of structure: or its pharmaceutically acceptable salts or prodrags thereof, in combination or alternation with one or more other antivirally effective agents, in the manufacture of a medicament for the treatment and prophylaxis of a hepatitis

C viras infection in a host.

46. Use of compound of stracture:

C viras infection in a host.

47. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of:

⁽0 (ϋ) (iii)

(iv) (v) (vi)

wherein A, G, and L are each independently CH or N;

D is N, CH, C-CN, C-NO₂, C-C_]-3 alkyl, C-NHCONH₂, C-CONQ 1"1Q11 , C- CSNQ^πQⁿ. CCOOQ¹¹, C-C(=NH)NH₂, C-hydroxy, C-Cι_-3alkoxy,C-amino, C-CM alkylamino, C-di(C_M alkyl)amino, C-halogen, C-(l,3-oxazol-2-yl), C-(l,3- thiazol-2-yl), or C-(imidazol-2-yl); wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and _-3 alkoxy; E is N or CQ⁵; W is O, S, orNR;

R is H, OH, alkyl;

Q⁶ is H, OH, SH, NH₂, C_M alkylamino, di(CM alkyl)amino, C_3-6 cycloalkylamino, halogen,

C_M alkyl, C_M alkoxy, or CF₃; Q⁵ is H, Cι-6 alkyl, C₂.₆ alkenyl, C_2-e alkynyl, C_M alkylamino, CF₃, halogen, N, CN, NO₂, NHCONHz, CONQ^uQ^π, CSNQⁿQⁿ, COOQ¹¹, C(=NH)NH₂, hydroxy, Cι- alkoxy,amino, CM alkylamino, di(Cι_-4 alkyl)amino, halogen, l,3-oxazol-2-yl, l,3-thiazol-2-yl, or imidazol-2-yl; wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and _-3 alkoxy;

Q⁷ and Q¹⁴ are each independently selected from the group consisting of H, CF₃, OH, SH, OR, SR C_M alkyl, amino, C_M alkylamino, C_3-e cycloalkylamino, and di(C alkyl)amino; Q^u is independently H or C ι _-6 alkyl;

Q⁸ is H, halogen, CN, carboxy, C_M alkyloxycarbonyl, N₃, amino, C alkylamino, di(C alkyl)amino, hydroxy, Cι_₆ alkoxy, Cue alkylthio, C e alkylsulfonyl, (CM alkyl)0-2 aminomethyl, N, CN, N0₂, Q_-3 alkyl, NHCONH₂, CONQ^πQ^u, CSNQ^uQⁿ, COOQ¹¹, C(=NH)NH₂, l,3-oxazol-2-yl, 1,3 -thiazolyl, or imidazol-2-yl, wherein alkyl is unsubstituted or substituted with one to three groups independently selected from halogen, amino, hydroxy, carboxy, and Cι_-3 alkoxy.

88. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of:

(D) (E)

wherein:

Ti and T₂ are independently selected from N, CH, or C-Q 16.

Q , U, and Y are independently selected from H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl, -O-alkyl, -O-alkenyl, -O- alkynyl, -O-aryl, -O-aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N-aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S- cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH₂, C0₂-alkyl, CONH-alkyl, CON- dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_mNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mNO₂, (CH₂)_mCONH₂, C_M alkylamino, di(C_M alkyl)amino, C₃.₆ cycloalkylamino, C alkoxy, C_M alkoxycarbonyl, C e alkylthio, Cue alkylsulfonyl, (C_M alkyl)o_-2 aminomethyl, or-NHC(=NH)NH₂;

R⁴ and R⁵ are independently selected from hydrogen, acyl, or alkyl; m is 0-10; Z is S, SQ, SO₂, C=0, or NQ²⁰; Q²⁰ is H or alkyl; and

Vi and V₂ are independently selected from CH or N;

89. A method of treatment or prophylaxis as in claims 3, 4, 13, or 14, in which the purine or pyrimidine base is selected from the group comprising of:

(F) (G) (H) (I) wherein:

T₃ and T₄ are independently selected from N or CQ²²;

Q²² is independently selected from H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵, Br-vinyl,-O-alkyl, -O-alkenyl, -O-alkynyl, -O-aryl, -O- aralkyl, -O-acyl, -O-cycloalkyl, NH₂, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N- aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S-cycloalkyl, S-aralkyl, CN, N₃, COOH, CONH₂, CO₂-alkyl, CONH-alkyl, CON-dialkyl, OH, CF₃, CH₂OH, (CH₂)_mOH, (CH₂)_mNH₂, (CH₂)_mCOOH, (CH₂)_mCN, (CH₂)_mNO₂, (CH₂)_mCONH₂, C_M alkylamino, di(C_Malkyl)amino, C_3-6 cycloalkylamino, C alkoxy, C alkoxycarbonyl, Cue alkylthio, C e alkylsulfonyl, (C_M alkyl)_0-2 aminomethyl, or -NHC(=NH)NH₂; R and R are independently selected from hydrogen, acyl, or alkyl; m is 0-10;

Tβ, T₇, T₈, T , Tio, T_H, and Tj₂ are independently selected from N or CH;

U is H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO- alkoxyalkyl, chloro, bromo, fluoro, iodo, OR⁴, NR⁴R⁵ or SR⁵;

Y₂ is O, S, NH, NR or CQ²⁴Q²⁶ where R is H, OH, or alkyl;